vim: Fix increment panicking due to invalid utf8 offsets (#43101)

Fixes ZED-3ER

Release Notes:

- Fixed a panic when using vim increment on a multibyte character
5052a460b4Lukas Wirth committed on 11/20/2025, 7:12:50 AM· committed by GitHubparent66382ac
1 file changedLine totals unavailable