USDZExporter: Store only objects with PBR Materials (#21847)

examples/js/exporters/USDZExporter.js

@@ -13,7 +13,7 @@
 			const textures = {};
 			scene.traverseVisible( object => {
 
-				if ( object.isMesh ) {
+				if ( object.isMesh && object.material.isMeshStandardMaterial ) {
 
 					const geometry = object.geometry;
 					const material = object.material;

examples/jsm/exporters/USDZExporter.js

@@ -17,7 +17,7 @@ class USDZExporter {
 
 		scene.traverseVisible( ( object ) => {
 
-			if ( object.isMesh ) {
+			if ( object.isMesh && object.material.isMeshStandardMaterial ) {
 
 				const geometry = object.geometry;
 				const material = object.material;