Assuming line 28 was deleted, the block header for a unified diff looks like:
+28,1 -27,0
This is true for usual suspects like `diff -U0` and `git diff -U0`, but
unfortunately not for Fossil. It would report this instead:
+28,1 -0,0
This lead our code to believe that line 1 instead of line 28 was deleted. And
maybe it's right about that. There does not seem to be a standard for patch/diff
output, but according to my knowledge Fossil is the only VCS doing that.
Anyway, this commit's change should make the detection of a deleted first line
work for every VCS again.
Fixes https://github.com/mhinz/vim-signify/issues/282
64b226cf1b