compositor: make sure to reset views' pointers to destroyed output

When an output is being destroyed reassign the output of the views
that were in it, to be sure not to keep a dangling pointer which could
be used later on by calling weston_surface_assign_output() on the
view's surface.
Also make sure we send wl_surface.leave events to the surfaces that
were in that output.

Reviewed-by: Jonas Ådahl <jadahl@gmail.com>

src/compositor.c

@@ -1079,6 +1079,9 @@ weston_view_assign_output(struct weston_view *ev)
 	mask = 0;
 	pixman_region32_init(&region);
 	wl_list_for_each(output, &ec->output_list, link) {
+		if (output->destroying)
+			continue;
+
 		pixman_region32_intersect(&region, &ev->transform.boundingbox,
 					  &output->region);
 
@@ -3888,9 +3891,15 @@ WL_EXPORT void
 weston_output_destroy(struct weston_output *output)
 {
 	struct wl_resource *resource;
+	struct weston_view *view;
 
 	output->destroying = 1;
 
+	wl_list_for_each(view, &output->compositor->view_list, link) {
+		if (view->output_mask & (1 << output->id))
+			weston_view_assign_output(view);
+	}
+
 	wl_event_source_remove(output->repaint_timer);
 
 	weston_presentation_feedback_discard_list(&output->feedback_list);