setup_git_directory(): fix move to worktree toplevel directory
When setup_git_directory() returns successfully, it is supposed to move
current working directory to worktree toplevel directory.
However, the code recomputing prefix inside setup_git_directory() has
to move cwd back to original working directory, in order to get new
prefix. After that, it should move cwd back to worktree toplevel
directory as expected.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>