Fix crash when view in scratchpad becomes urgent

sway/tree/view.c

@@ -1028,8 +1028,10 @@ void view_set_urgent(struct sway_view *view, bool enable) {
 
 	ipc_event_window(view->container, "urgent");
 
+	if (view->container->workspace) {
 		workspace_detect_urgent(view->container->workspace);
 	}
+}
 
 bool view_is_urgent(struct sway_view *view) {
 	return view->urgent.tv_sec || view->urgent.tv_nsec;