From: Orgad Shaneh <orgads@gmail.com>

If you open 2 git gui instances in the same directory, then close one
of them and try to close the other, an error message pops up, saying:
'error renaming ".git/GITGUI_BCK": no such file or directory', and it
is no longer possible to close the window ever.

Fix by catching this error, and proceeding even if the file no longer
exists.

Signed-off-by: Orgad Shaneh <orgads@gmail.com>

Submitted-As: https://lore.kernel.org/git/pull.1446.git.git.1675239967804.gitgitgadget@gmail.com