fix: handle line codes with an empty line number

[Enceradeira]

Opening a file in the reviewer that has a multi-line discussion fails in the DiffviewDiffBufWinEnter hook:

gitlab.nvim: Error setting diagnostics: .../gitlab/actions/common.lua:268: attempt to perform arithmetic on local 'new_end_line' (a nil value)

parse_line_code matches %w+_(%d+)_(%d+) and returns nil, nil when either number of the line code is empty (e.g. <sha>__44, as GitLab produces when a line has no counterpart on the other side). get_line_numbers_for_range then does arithmetic on the nil values; the old-SHA branch (line 265) has the same problem.

Changes

• parse_line_code accepts empty numbers (%d*) and returns nil for them; a nil line code no longer throws.
• get_line_numbers_for_range falls back to a single-line range when either end of the range has no number (old-SHA and new-SHA branches).
• Adds tests/spec/line_code_spec.lua, which reproduces the error without the fix.

🤖 Generated with Claude Code

[jakubbortlik]

Hi @Enceradeira, are these empty line numbers created by gitlab.nvim or by Gitlab in the browser? I'm asking because maybe this is not the right place to fix this. If the missing line numbers are caused by gitlab.nvim, then we should fix the line code creation.

[jakubbortlik]

By the way there is #587 - is it solving the same problem? The author of that other PR never replied to my question, so I didn't bother to merge it :)