Problem: diff mode does not handle overlapping diffs correctly
Solution: correct the logic to handle overlapping blocks
(Yukihiro Nakadaira)
Vim merges overlapped diff blocks and it doesn't work expectedly
in some situation.
closes: #15735
Signed-off-by: Yukihiro Nakadaira <yukihiro.nakadaira@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
