git: do not mix in_git_dir with eval{}

git: do not mix in_git_dir with eval{}

If we throw an exception (usually from run_or_die), in_git_dir won't
unshift the current directory from the stack. That's usually fine,
but in rcs_preprevert we catch exceptions and do some cleanup before
returning, for which we need the git directory to be the root and
not the temporary working tree.

(cherry picked from commit 650445645430931bea5947a217fa425b0ca3b521)