language: Fix `HighlightedText::first_line_preview` creating incorrect highlight ranges (#39705)

Fixes ZED-1XW

Release Notes:

- N/A *or* Added/Fixed/Improved ...
642643de01Lukas Wirth committed on 10/7/2025, 6:52:59 PM· committed by GitHubparent391e304
1 file changedLine totals unavailable