"git-local-fetch -s" did not work with a packed repository, because
symlink() happily created a link to a non-existing object file,
therefore fetch_file() always returned success, and fetch_pack() was
not called. Fixed by calling stat() before symlink() to ensure the
file really exists.
Signed-off-by: Sergey Vlasov <vsu@altlinux.ru> Signed-off-by: Junio C Hamano <junkio@cox.net>