gltf: Fail gracefully when a mesh instance fails.

(cherry picked from commit 5a9eee6b1a2f633935cfcbbe5f938263dd092e8e)

editor/import/editor_scene_importer_gltf.cpp

@@ -3138,13 +3138,15 @@ void EditorSceneImporterGLTF::_process_mesh_instances(GLTFState &state, Spatial
 			const GLTFSkinIndex skin_i = node->skin;
 
 			Map<GLTFNodeIndex, Node *>::Element *mi_element = state.scene_nodes.find(node_i);
+			ERR_CONTINUE_MSG(mi_element == nullptr, vformat("Unable to find node %d", node_i));
+
 			MeshInstance *mi = Object::cast_to<MeshInstance>(mi_element->get());
-			ERR_FAIL_COND(mi == nullptr);
+			ERR_CONTINUE_MSG(mi == nullptr, vformat("Unable to cast node %d of type %s to MeshInstance", node_i, mi_element->get()->get_class_name()));
 
 			const GLTFSkeletonIndex skel_i = state.skins[node->skin].skeleton;
 			const GLTFSkeleton &gltf_skeleton = state.skeletons[skel_i];
 			Skeleton *skeleton = gltf_skeleton.godot_skeleton;
-			ERR_FAIL_COND(skeleton == nullptr);
+			ERR_CONTINUE_MSG(skeleton == nullptr, vformat("Unable to find Skeleton for node %d skin %d", node_i, skin_i));
 
 			mi->get_parent()->remove_child(mi);
 			skeleton->add_child(mi);