CCEventDispatcher crash fix

Fix possible crashes which could be caused by the EventDispatcher having listeners associated with nodes are destroyed. Catch the case where a node registers a listener while we are dispatching events and gets destroyed while that event is still being dispatched. Check the list of nodes to be added into the event dispatcher fully when we are cleaning listeners for a target node.

This issue was found using the extra debug verification in this pull request:
https://github.com/cocos2d/cocos2d-x/pull/6011