fix Flow.take waiting for n+1 elements instead of terminating at n

[ZbutwialyPiernik]

Previously, take(n) would hang forever if the source had exactly n elements. This happened because it tried to read one more element (to check if it should break) even after taking all n elements it needed.

For example, take(3) on a 3-element stream would:

1. Take element 1
2. Take element 2
3. Take element 3
4. Try to read element 4... and wait forever

Now it breaks right after taking the n-th element, without trying to read more:

Added test shouldBreakImmediatelyAfterTakingNElements() that verifies we process exactly 3 elements when calling take(3), not 4.

[adamw]

Thanks!