GLTFLoader.js : Update WebP Texture Loader (#23823)

Replace parameter 2 to parser.loadTextureImage with extension.source (it must be an index, not an object)

examples/jsm/loaders/GLTFLoader.js

@@ -1116,7 +1116,7 @@ class GLTFTextureWebPExtension {
 
 		return this.detectSupport().then( function ( isSupported ) {
 
-			if ( isSupported ) return parser.loadTextureImage( textureIndex, source, loader );
+			if ( isSupported ) return parser.loadTextureImage( textureIndex, extension.source, loader );
 
 			if ( json.extensionsRequired && json.extensionsRequired.indexOf( name ) >= 0 ) {