Create an empty group if a loaded glb contains no scene (#1040)

* Create an empty group if a loaded glb contains no scene

* remove unnecessary changes

* Update TilesRenderer.js

Author: WilliamLiu-1997

src/three/TilesRenderer.js

@@ -11,6 +11,7 @@ import {
 	Euler,
 	LoadingManager,
 	EventDispatcher,
+	Group,
 } from 'three';
 import { raycastTraverse, raycastTraverseFirstHit } from './raycastTraverse.js';
 import { readMagicBytes } from '../utilities/readMagicBytes.js';
@@ -660,6 +661,7 @@ export class TilesRenderer extends TilesRendererBase {
 					// any transformations applied to it can be assumed to be applied after load
 					// (such as applying RTC_CENTER) meaning they should happen _after_ the z-up
 					// rotation fix which is why "multiply" happens here.
+					result.scene = result.scene || new Group();
 					const { scene } = result;
 					scene.updateMatrix();
 					scene.matrix