wlr_seat_touch: Destroy the touchpoint on client destroy

Since e26217c51e3a5e1d7dfc95a8a76299e056497981, touchpoints can outlive
surfaces. This works fine as long as the client stays around, but fails
horribly otherwise; therefore we have to make sure that touchpoints don't
outlive their clients.

Fixes #1788

include/wlr/types/wlr_seat.h

@@ -64,6 +64,7 @@ struct wlr_touch_point {
 
 	struct wl_listener surface_destroy;
 	struct wl_listener focus_surface_destroy;
+	struct wl_listener client_destroy;
 
 	struct {
 		struct wl_signal destroy;

types/seat/wlr_seat_touch.c

@@ -101,6 +101,7 @@ static void touch_point_destroy(struct wlr_touch_point *point) {
 
 	touch_point_clear_focus(point);
 	wl_list_remove(&point->surface_destroy.link);
+	wl_list_remove(&point->client_destroy.link);
 	wl_list_remove(&point->link);
 	free(point);
 }
@@ -115,6 +116,13 @@ static void touch_point_handle_surface_destroy(struct wl_listener *listener,
 	wl_list_init(&point->surface_destroy.link);
 }
 
+static void touch_point_handle_client_destroy(struct wl_listener *listener,
+		void *data) {
+	struct wlr_touch_point *point =
+		wl_container_of(listener, point, client_destroy);
+	touch_point_destroy(point);
+}
+
 static struct wlr_touch_point *touch_point_create(
 		struct wlr_seat *seat, int32_t touch_id,
 		struct wlr_surface *surface, double sx, double sy) {
@@ -143,7 +151,8 @@ static struct wlr_touch_point *touch_point_create(
 
 	wl_signal_add(&surface->events.destroy, &point->surface_destroy);
 	point->surface_destroy.notify = touch_point_handle_surface_destroy;
-
+	wl_signal_add(&client->events.destroy, &point->client_destroy);
+	point->client_destroy.notify = touch_point_handle_client_destroy;
 	wl_list_insert(&seat->touch_state.touch_points, &point->link);
 
 	return point;