Problem:
Some language servers (e.g., rust-analyzer, texlab) are desynced when
the user deletes the entire contents of the buffer. This is due to the
discrepancy between how nvim computes diff and how nvim treats empty
buffer.
* diff: If the buffer became empty, then the diff includes the last
line's eol.
* empty buffer: Even if the buffer is empty, nvim regards it as having
a single empty line with eol.
Solution:
Add special case for diff computation when the buffer becomes empty so
that it does not include the eol of the last line.
6bb40f3dbf