lock: listen to the correct map signal

sway/lock.c

@@ -104,7 +104,7 @@ static void handle_new_surface(struct wl_listener *listener, void *data) {
 	surf->surface = lock_surface->surface;
 	surf->output = output;
 	surf->map.notify = handle_surface_map;
-	wl_signal_add(&lock_surface->events.map, &surf->map);
+	wl_signal_add(&lock_surface->surface->events.map, &surf->map);
 	surf->destroy.notify = handle_surface_destroy;
 	wl_signal_add(&lock_surface->events.destroy, &surf->destroy);
 	surf->surface_commit.notify = handle_surface_commit;