tools/mpris-proxy: unregister object path if player registration fails

The `owner' string, passed as user data, is freed if the player fails
registration, but the object path still exists. Upon program exiting,
the lingering path will be enumerated and the attached user data will be
freed again.

tools/mpris-proxy.c

@@ -480,6 +480,7 @@ static void add_player(DBusConnection *conn, const char *name,
 	reply = dbus_connection_send_with_reply_and_block(sys, msg, -1, &err);
 	if (!reply) {
 		fprintf(stderr, "Can't register player\n");
+		dbus_connection_unregister_object_path(sys, path);
 		free(owner);
 		if (dbus_error_is_set(&err)) {
 			fprintf(stderr, "%s\n", err.message);