Problem: in email-quoted diffs (qw > 0), the body prefix DiffsClear only
covered col 0..qw (the quote prefix). The diff prefix marker column at
col qw..pw+qw had no DiffsClear, leaving a 1-column gap where native
treesitter background could bleed through on context lines.
Solution: extend body prefix DiffsClear end_col from qw to pw + qw,
covering both the quote prefix and the diff prefix marker. On +/- lines
this was already masked by DiffsAdd/DiffsDelete at higher priority, but
context lines (prefix ' ') had no such mask.
Closes#142 issue 1.
Barrett Ruth
0bf1229a66
