GLTFLoader: Throw unhandled errors.

examples/js/loaders/GLTFLoader.js

@@ -40,8 +40,11 @@ THREE.GLTFLoader = ( function () {
 
 					if ( onError !== undefined ) {
 
-						// For SyntaxError or TypeError, return a generic failure message.
-						onError( e.constructor === Error ? e : new Error( 'THREE.GLTFLoader: Unable to parse model.' ) );
+						onError( e );
+
+					} else {
+
+						throw e;
 
 					}