bugfix for UI animation playing crash if GUI JSON file is loaded again.

_actionDic is a std::unordered_map, the insert() function will not work if the key is already existed. If a UI JSON file is loaded by GUIReader more than once, the animation information should update in the internal _actionDic map, as the rootWidget pointer is different.

...Detail see: http://blog.segmentfault.com/hongliang/1190000000659937