Fixes https://github.com/zed-industries/zed/issues/26039

Release Notes:

- Fixed an issue where diffs stopped updating closing and reopening them
after staging hunks.
- Fixed a bug where staging a hunk while the cursor was in a deleted
line would move the cursor erroneously.

---------

Co-authored-by: Cole Miller <m@cole-miller.net>
Co-authored-by: João Marcos <marcospb19@hotmail.com>