Negative index cut after fetch

[dhilt]

The following log reveals a problem with indexes after fetch & render:

going to fetch 10 items started from index -13
resolved 7 items (index = -13, count = 10)
stat before new items render, pos: 42, size: 1020, bwd_p: 80, fwd_p: 320, default: 20, items: 31, range: [-3..27]
stat after new items render, pos: 42, size: 1160, bwd_p: 80, fwd_p: 320, default: 20, items: 38, range: [-14..27]

Full log

```
adapter: reload() of 1.6
fallback startIndex to settings.startIndex (1)
setting scroll position at 0 [cancelled]
   ~~~ WF Cycle 1-88 STARTED ~~~  
---=== loop 1-88-155 start
skipping fetch backward direction [initial loop]
forcing fetch forward direction [no item size]
fetch interval: [1..5]
fetch direction is "forward"
going to fetch 5 items started from index 1
resolved 5 items (index = 1, count = 5)
stat before new items render, pos: 0, size: 300, bwd_p: 0, fwd_p: 300, default: no, items: 0, range: no
⤵ 0 0ms 
skipping scroll 0 [pending]
default size has been updated: 20
stat after new items render, pos: 0, size: 400, bwd_p: 0, fwd_p: 300, default: 20, items: 5, range: [1..5]
skipping clip [initial cycle]
forward padding will be increased by 200 to fill the viewport
stat after paddings adjustments, pos: 0, size: 300, bwd_p: 0, fwd_p: 200, default: 20, items: 5, range: [1..5]
---=== loop 1-88-155 done, loop 1-88-156 start
start delta is 0
fetch interval: [-7..23]
fetch interval after Buffer flushing: [6..23]
fetch direction is "forward"
going to fetch 18 items started from index 6
resolved 18 items (index = 6, count = 18)
stat before new items render, pos: 0, size: 300, bwd_p: 0, fwd_p: 200, default: 20, items: 5, range: [1..5]
stat after new items render, pos: 0, size: 660, bwd_p: 0, fwd_p: 200, default: 20, items: 23, range: [1..23]
skipping clip [initial cycle]
stat after paddings adjustments, pos: 0, size: 460, bwd_p: 0, fwd_p: 0, default: 20, items: 23, range: [1..23]
first index = 1, delta = 0
---=== loop 1-88-156 done, loop 1-88-157 start
start delta is 0
fetch interval: [-7..23]
fetch interval after Buffer flushing: [-7..0]
going to fetch 8 items started from index -7
resolved 8 items (index = -7, count = 8)
stat before new items render, pos: 0, size: 460, bwd_p: 0, fwd_p: 0, default: 20, items: 23, range: [1..23]
stat after new items render, pos: 0, size: 620, bwd_p: 0, fwd_p: 0, default: 20, items: 31, range: [-7..23]
skipping clip [initial cycle]
stat after paddings adjustments, pos: 0, size: 620, bwd_p: 0, fwd_p: 0, default: 20, items: 31, range: [-7..23]
first index = 1, delta = 0
setting scroll position at 160
stat after scroll adjustment, pos: 160, size: 620, bwd_p: 0, fwd_p: 0, default: 20, items: 31, range: [-7..23]
---=== loop 1-88-157 done, loop 1-88-158 start
start delta is 160
fetch interval: [-7..23]
fetch interval after Buffer flushing: no
---=== loop 1-88-158 done
   ~~~ WF Cycle 1-88 FINALIZED ~~~  
skipping scroll 160 [synthetic]
⤵ 206 0ms 
   ~~~ WF Cycle 1-89 STARTED ~~~  
---=== loop 1-89-159 start
start delta is 160
fetch interval: [-5..25]
fetch interval after Buffer flushing: [24..25]
fetch interval after bufferSize adjustment: [24..28]
fetch direction is "forward"
going to fetch 5 items started from index 24
resolved 5 items (index = 24, count = 5)
stat before new items render, pos: 206, size: 620, bwd_p: 0, fwd_p: 0, default: 20, items: 31, range: [-7..23]
stat after new items render, pos: 206, size: 720, bwd_p: 0, fwd_p: 0, default: 20, items: 36, range: [-7..28]
looking for anti-forward items that are out of [-5..28] range
stat before clip (46), pos: 206, size: 720, bwd_p: 0, fwd_p: 0, default: 20, items: 36, range: [-7..28]
clipped 2 item(s) from Buffer, +40 fwd px, range: [-7..-6]
stat after clip, pos: 206, size: 720, bwd_p: 40, fwd_p: 0, default: 20, items: 34, range: [-5..28]
stat after paddings adjustments, pos: 206, size: 720, bwd_p: 40, fwd_p: 0, default: 20, items: 34, range: [-5..28]
first index = 3, delta = -6
---=== loop 1-89-159 done, loop 1-89-160 start
start delta is 160
fetch interval: [-5..25]
fetch interval after Buffer flushing: no
---=== loop 1-89-160 done
   ~~~ WF Cycle 1-89 FINALIZED ~~~  
⤵ 293 26ms / 14ms delay
⤵ 293 16ms triggered by timer set on 293
   ~~~ WF Cycle 1-90 STARTED ~~~  
---=== loop 1-90-161 start
start delta is 160
fetch interval: [0..30]
fetch interval after Buffer flushing: [29..30]
fetch interval after bufferSize adjustment: [29..33]
fetch direction is "forward"
going to fetch 5 items started from index 29
resolved 5 items (index = 29, count = 5)
stat before new items render, pos: 293, size: 720, bwd_p: 40, fwd_p: 0, default: 20, items: 34, range: [-5..28]
⤵ 420 20ms / 20ms delay
stat after new items render, pos: 420, size: 820, bwd_p: 40, fwd_p: 0, default: 20, items: 39, range: [-5..33]
looking for anti-forward items that are out of [0..33] range
stat before clip (47), pos: 420, size: 820, bwd_p: 40, fwd_p: 0, default: 20, items: 39, range: [-5..33]
clipped 5 item(s) from Buffer, +100 fwd px, range: [-5..-1]
stat after clip, pos: 420, size: 820, bwd_p: 140, fwd_p: 0, default: 20, items: 34, range: [0..33]
stat after paddings adjustments, pos: 420, size: 820, bwd_p: 140, fwd_p: 0, default: 20, items: 34, range: [0..33]
first index = 7, delta = -13
shift position due to fetch-render difference (127)
---=== loop 1-90-161 done, loop 1-90-162 start
start delta is 160
fetch interval: [6..36]
fetch interval after Buffer flushing: [34..36]
fetch interval after bufferSize adjustment: [34..38]
fetch direction is "forward"
going to fetch 5 items started from index 34
resolved 5 items (index = 34, count = 5)
stat before new items render, pos: 420, size: 820, bwd_p: 140, fwd_p: 0, default: 20, items: 34, range: [0..33]
stat after new items render, pos: 420, size: 920, bwd_p: 140, fwd_p: 0, default: 20, items: 39, range: [0..38]
looking for anti-forward items that are out of [6..38] range
stat before clip (48), pos: 420, size: 920, bwd_p: 140, fwd_p: 0, default: 20, items: 39, range: [0..38]
clipped 6 item(s) from Buffer, +120 fwd px, range: [0..5]
stat after clip, pos: 420, size: 920, bwd_p: 260, fwd_p: 0, default: 20, items: 33, range: [6..38]
stat after paddings adjustments, pos: 420, size: 920, bwd_p: 260, fwd_p: 0, default: 20, items: 33, range: [6..38]
first index = 14, delta = 0
---=== loop 1-90-162 done, loop 1-90-163 start
start delta is 160
fetch interval: [6..36]
fetch interval after Buffer flushing: no
---=== loop 1-90-163 done
   ~~~ WF Cycle 1-90 FINALIZED ~~~  
⤵ 420 21ms triggered by timer set on 420
   ~~~ WF Cycle 1-91 STARTED ~~~  
---=== loop 1-91-164 start
start delta is 160
fetch interval: [6..36]
fetch interval after Buffer flushing: no
---=== loop 1-91-164 done
   ~~~ WF Cycle 1-91 FINALIZED ~~~  
⤵ 494 30ms / 10ms delay
⤵ 494 12ms triggered by timer set on 494
   ~~~ WF Cycle 1-92 STARTED ~~~  
---=== loop 1-92-165 start
start delta is 160
fetch interval: [10..40]
fetch interval after Buffer flushing: [39..40]
fetch interval after bufferSize adjustment: [39..43]
fetch direction is "forward"
going to fetch 5 items started from index 39
resolved 5 items (index = 39, count = 5)
stat before new items render, pos: 494, size: 920, bwd_p: 260, fwd_p: 0, default: 20, items: 33, range: [6..38]
stat after new items render, pos: 494, size: 1020, bwd_p: 260, fwd_p: 0, default: 20, items: 38, range: [6..43]
looking for anti-forward items that are out of [10..43] range
stat before clip (49), pos: 494, size: 1020, bwd_p: 260, fwd_p: 0, default: 20, items: 38, range: [6..43]
clipped 4 item(s) from Buffer, +80 fwd px, range: [6..9]
stat after clip, pos: 494, size: 1020, bwd_p: 340, fwd_p: 0, default: 20, items: 34, range: [10..43]
stat after paddings adjustments, pos: 494, size: 1020, bwd_p: 340, fwd_p: 0, default: 20, items: 34, range: [10..43]
first index = 17, delta = -14
---=== loop 1-92-165 done, loop 1-92-166 start
start delta is 160
fetch interval: [10..40]
fetch interval after Buffer flushing: no
---=== loop 1-92-166 done
   ~~~ WF Cycle 1-92 FINALIZED ~~~  
⤵ 530 17ms / 23ms delay
⤵ 523 34ms delayed
⤵ 523 23ms triggered by timer set on 530
   ~~~ WF Cycle 1-93 STARTED ~~~  
---=== loop 1-93-167 start
start delta is 160
fetch interval: [11..41]
fetch interval after Buffer flushing: no
---=== loop 1-93-167 done
   ~~~ WF Cycle 1-93 FINALIZED ~~~  
⤴ 486 16ms / 24ms delay
⤴ 244 33ms delayed
⤴ 244 25ms triggered by timer set on 486
   ~~~ WF Cycle 1-94 STARTED ~~~  
---=== loop 1-94-168 start
start delta is 160
fetch interval: [-3..27]
fetch interval after Buffer flushing: [-3..9]
fetch direction is "backward"
going to fetch 13 items started from index -3
resolved 13 items (index = -3, count = 13)
stat before new items render, pos: 244, size: 1020, bwd_p: 340, fwd_p: 0, default: 20, items: 34, range: [10..43]
stat after new items render, pos: 244, size: 1280, bwd_p: 340, fwd_p: 0, default: 20, items: 47, range: [-3..43]
looking for anti-backward items that are out of [-3..27] range
stat before clip (50), pos: 244, size: 1280, bwd_p: 340, fwd_p: 0, default: 20, items: 47, range: [-3..43]
clipped 16 item(s) from Buffer, +320 bwd px, range: [28..43]
stat after clip, pos: 244, size: 1280, bwd_p: 340, fwd_p: 320, default: 20, items: 31, range: [-3..27]
stat after paddings adjustments, pos: 244, size: 1020, bwd_p: 80, fwd_p: 320, default: 20, items: 31, range: [-3..27]
first index = 5, delta = -4
---=== loop 1-94-168 done, loop 1-94-169 start
start delta is 160
fetch interval: [-3..27]
fetch interval after Buffer flushing: no
---=== loop 1-94-169 done
   ~~~ WF Cycle 1-94 FINALIZED ~~~  
⤴ 243 16ms / 24ms delay
⤴ 42 33ms delayed
⤴ 42 25ms triggered by timer set on 243
   ~~~ WF Cycle 1-95 STARTED ~~~  
---=== loop 1-95-170 start
start delta is 160
fetch interval: [-13..17]
fetch interval after Buffer flushing: [-13..-4]
fetch direction is "backward"
going to fetch 10 items started from index -13
resolved 7 items (index = -13, count = 10)
stat before new items render, pos: 42, size: 1020, bwd_p: 80, fwd_p: 320, default: 20, items: 31, range: [-3..27]
stat after new items render, pos: 42, size: 1160, bwd_p: 80, fwd_p: 320, default: 20, items: 38, range: [-14..27]
looking for anti-backward items that are out of [-13..17] range
skipping clip [no items to clip]
stat after paddings adjustments, pos: 42, size: 760, bwd_p: 0, fwd_p: 0, default: 20, items: 38, range: [-14..27]
first index = -5, delta = -2
skipping scroll 0 [pre-synthetic]
setting scroll position at 98
stat after scroll adjustment (-42), pos: 98, size: 760, bwd_p: 0, fwd_p: 0, default: 20, items: 38, range: [-14..27]
---=== loop 1-95-170 done, loop 1-95-171 start
start delta is 300
fetch interval: [-17..-8]
fetch interval after Buffer flushing: [-17..-15]
fetch interval after bufferSize adjustment: [-19..-15]
fetch direction is "backward"
going to fetch 5 items started from index -19
resolved 0 items (index = -19, count = 5)
---=== loop 1-95-171 done
   ~~~ WF Cycle 1-95 FINALIZED ~~~  
synthetic scroll has been fulfilled: 0 < 98
⤴ 0 34ms / 6ms delay
⤴ 0 6ms triggered by timer set on 0
   ~~~ WF Cycle 1-96 STARTED ~~~  
---=== loop 1-96-172 start
start delta is 300
fetch interval: [-14..-8]
fetch interval after Buffer flushing: no
---=== loop 1-96-172 done
   ~~~ WF Cycle 1-96 FINALIZED ~~~  
adapter: showLog()
```

Expecting result after render should be [-10..27].

This PR provides the relevant test specification, reproducing the case.