Fix possible uninitialized var in memline.c

[chrisbra]

With gcc on msys64:
,----
| $ gcc --version
| gcc.exe (Rev6, Built by MSYS2 project) 13.1.0
| Copyright (C) 2023 Free Software Foundation, Inc. | This is free software; see the source for copying conditions. There is NO | warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. `----

I see the following warning in memline.c:

,----
| memline.c: In function 'adjust_text_props_for_delete': | memline.c:3670:43: warning: 'this_props_len' may be used uninitialized [-Wmaybe-uninitialized]
| 3670 | for (done_this = 0; done_this < this_props_len;
| | ~~~~~~~~~~^~~~~~~~~~~~~~~~
| memline.c:3629:17: note: 'this_props_len' was declared here
| 3629 | int this_props_len;
| | ^~~~~~~~~~~~~~
| In file included from memline.c:45:
| memline.c:3677:56: warning: 'text' may be used uninitialized [-Wmaybe-uninitialized]
| 3677 | mch_memmove(&prop_this, text + textlen + done_this,
| vim.h:1803:66: note: in definition of macro 'mch_memmove'
| 1803 | # define mch_memmove(to, from, len) memmove((char*)(to), (char*)(from), (size_t)(len))
| | ^~~~
| memline.c:3630:18: note: 'text' was declared here
| 3630 | char_u text;
| | ^~~~
| memline.c:3677:56: warning: 'textlen' may be used uninitialized [-Wmaybe-uninitialized]
| 3677 | mch_memmove(&prop_this, text + textlen + done_this,
| | ^
| vim.h:1803:66: note: in definition of macro 'mch_memmove'
| 1803 | # define mch_memmove(to, from, len) memmove((char)(to), (char*)(from), (size_t)(len))
| | ^~~~
| memline.c:3631:17: note: 'textlen' was declared here
| 3631 | size_t textlen;
| | ^~~~~~~
`----

Interestingly the other warnings go away, after fixing the first one and initializing this_prop_len.

But I think this may be worth it anyhow to fix this warning.

[codecov]

Codecov Report

Merging #12599 (57d750a) into master (590aae3) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #12599      +/-   ##
==========================================
- Coverage   82.09%   82.08%   -0.01%     
==========================================
  Files         160      160              
  Lines      193658   193659       +1     
  Branches    43482    43482              
==========================================
- Hits       158977   158960      -17     
- Misses      21836    21853      +17     
- Partials    12845    12846       +1     

Flag	Coverage Δ
huge-clang-none	82.71% <100.00%> (-0.02%)	⬇️
linux	82.71% <100.00%> (-0.02%)	⬇️
mingw-x64-HUGE	76.61% <ø> (-0.01%)	⬇️
mingw-x86-HUGE	77.07% <ø> (+0.01%)	⬆️
windows	78.20% <ø> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/memline.c	80.44% <100.00%> (+<0.01%)	⬆️

... and 9 files with indirect coverage changes