Fix CaptureDiffNotePositionService when position is nil
What does this MR do?
Fix CaptureDiffNotePositionService when position is nil
When a note is outdated, the position returned from PositionTracker
is nil
: https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/diff/position_tracer/line_strategy.rb#L173
We need to handle such a case: #215487 (closed)