unix-socket: remove stale socket before calling chdir()

unix_stream_listen() is given a path.  It calls unix_sockaddr_init(),
which in turn can call chdir().  After that a relative path doesn't
mean the same as before.  Any use of the original path should thus
happen before that call.  For that reason, unlink the given path
(to get rid of a possibly existing stale socket) right at the
beginning of the function.

Noticed-by: Karsten Blees <karsten.blees@gmail.com>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

unix-socket.c

@@ -99,11 +99,12 @@ int unix_stream_listen(const char *path)
 	struct sockaddr_un sa;
 	struct unix_sockaddr_context ctx;
 
+	unlink(path);
+
 	if (unix_sockaddr_init(&sa, path, &ctx) < 0)
 		return -1;
 	fd = unix_stream_socket();
 
-	unlink(path);
 	if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0)
 		goto fail;