修复obj补间动画的问题

src/support/Tween.ts

@@ -149,8 +149,8 @@ export class Tween extends HashObject {
 		this.loop = options ? options.loop : 0;
 		this.autoPlay = options ? (options.hasOwnProperty('autoPlay') ? options.autoPlay : true) : true;
 		this.fields = options ? options.fields : null;
-		this.onLoopComplete = options.onLoopComplete;
-		this.onComplete = options.onComplete;
+		this.onLoopComplete = options ? options.onLoopComplete : null;
+		this.onComplete = options ? options.onComplete : null;
 
 		this.plugins = plugins;