Fixes a bug where an event handler is called when no targetObject exists on hiding a poplist

Click a select -> select an option -> wait for the poplist to hide -> click outside -> $ called on undefined error. See the gif below:

![cry](http://recordit.co/tOQT8OFNot.gif)

Traces to here in eui-poplist.coffee:

      hide: ->
        # Only hide if a targetOject exists to hide in the first place
        if @get('targetObject')? 
          @animateOut({
            target: @get('targetObject').$()
            complete: => @breakdown()
          })   

So for some reason the event handler for click.ember-ui gets called - but no targetObject exists. My fix just guards hide() so it only executes if targetObject exists - but this seems bandaid-y.