Fix filehandle leak in "git branch -D"

On Windows (it can't touch open files in any way) the following fails:

    git branch -D branch1 branch2

if the both branches are in packed-refs.
Signed-off-by: NAlex Riesen <raa.lkml@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

refs.c

@@ -869,6 +869,7 @@ static int repack_without_ref(const char *refname)
 			die("too long a refname '%s'", list->name);
 		write_or_die(fd, line, len);
 	}
+	close(fd);
 	return commit_lock_file(&packlock);
 }