Merge pull request #3743 from RedSoxFan/fix-output-get-active-workspace

output_get_active_workspace: check workspaces length

sway/desktop/output.c

@@ -320,6 +320,9 @@ struct sway_workspace *output_get_active_workspace(struct sway_output *output) {
 	struct sway_seat *seat = input_manager_current_seat();
 	struct sway_node *focus = seat_get_active_tiling_child(seat, &output->node);
 	if (!focus) {
+		if (!output->workspaces->length) {
+			return NULL;
+		}
 		return output->workspaces->items[0];
 	}
 	return focus->sway_workspace;