Fix crash in GLTFNode.get_scene_node_path

(cherry picked from commit c77ba84d6fee2dfcaa5fe0ece77ce1f687053acb)

modules/gltf/structures/gltf_node.cpp

@@ -212,6 +212,7 @@ void GLTFNode::set_additional_data(const StringName &p_extension_name, Variant p
 }
 
 NodePath GLTFNode::get_scene_node_path(Ref<GLTFState> p_state, bool p_handle_skeletons) {
+	ERR_FAIL_COND_V_MSG(p_state.is_null(), NodePath(), "Cannot get scene node path because GLTFState is null.");
 	Vector<StringName> path;
 	Vector<StringName> subpath;
 	Ref<GLTFNode> current_gltf_node = this;