Fix eventHandlers length was wrong

LWF's eventHandlers length become wrong when use this pattern.

   lwf.addEventHandler('fooEvent', ->
     lwf.removeEventHandler('fooEvent', arguments.callee)
     doSomeThing()
   )

The handler execute logic gets loop count from eventHandlers.length at before execute loop.  
But handler function removes handler from eventHandlers in loop.
https://github.com/gree/lwf/blob/master/coffee/js_debug/lwf.js#L6749