Fix crash when joining two consecutive lines (#10000)

Release notes:

- Fixed a crash when joining two consecutive lines
([#9692](https://github.com/zed-industries/zed/pull/9692)).


This crash is not caused by `vim` or `editor`'s code logic, `join_line`
logic is okay, I found that the crash is caused by a refresh of git
`diff` after every update, hhen git diff generates hunks, it will look
for the cursor to the beginning of a line, and judge that if the cursor
result column is greater than 0, that is, it is not the beginning of a
line, it will correct the row to the next line, I think before we forgot
here that I need to adjust the column to 0 at the same time, otherwise
it is easy to go out of bounds, I am not sure if I need to add more
tests for this method, I can add if I need to, but I feel that this case
is a bit extreme

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Co-authored-by: Thorsten Ball <mrnugget@gmail.com>