ipc: handle NULL cases for node_get_output

sway/ipc-json.c

@@ -316,9 +316,12 @@ static void focus_inactive_children_iterator(struct sway_node *node,
 	struct focus_inactive_data *data = _data;
 	json_object *focus = data->object;
 	if (data->node == &root->node) {
-		int len = json_object_array_length(focus);
 		struct sway_output *output = node_get_output(node);
+		if (output == NULL) {
+			return;
+		}
 		size_t id = output->node.id;
+		int len = json_object_array_length(focus);
 		for (int i = 0; i < len; ++i) {
 			if ((size_t) json_object_get_int(json_object_array_get_idx(focus, i)) == id) {
 				return;

sway/tree/node.c

@@ -74,8 +74,10 @@ void node_get_box(struct sway_node *node, struct wlr_box *box) {
 
 struct sway_output *node_get_output(struct sway_node *node) {
 	switch (node->type) {
-	case N_CONTAINER:
+	case N_CONTAINER: {
-		return node->sway_container->workspace->output;
+		struct sway_workspace *ws = node->sway_container->workspace;
+		return ws ? ws->output : NULL;
+    }
 	case N_WORKSPACE:
 		return node->sway_workspace->output;
 	case N_OUTPUT: