update button scaler to fix audioMng not found issue.

Author: nantas

assets/scripts/UI/ButtonScaler.js

@@ -10,14 +10,16 @@ cc.Class({
     onLoad: function () {
         var self = this;
         var audioMng = cc.find('Menu/AudioMng') || cc.find('Game/AudioMng')
-        audioMng = audioMng.getComponent('AudioMng');
+        if (audioMng) {
+            audioMng = audioMng.getComponent('AudioMng');
+        }
         self.initScale = this.node.scale;
         self.button = self.getComponent(cc.Button);
         self.scaleDownAction = cc.scaleTo(self.transDuration, self.pressedScale);
         self.scaleUpAction = cc.scaleTo(self.transDuration, self.initScale);
         function onTouchDown (event) {
             this.stopAllActions();
-            audioMng.playButton();
+            if (audioMng) audioMng.playButton();
             this.runAction(self.scaleDownAction);
         }
         function onTouchUp (event) {