file_finder: Fix highlighting panic in open path prompt (#41808)

Closes https://github.com/zed-industries/zed/issues/41249

Couldn't quite come up with a test case here but verified it works.

Release Notes:

- Fixed a panic in file finder when deleting characters
50504793e6Lukas Wirth committed on 11/3/2025, 12:07:13 PM· committed by GitHubparentb625263
1 file changedLine totals unavailable