Plain Object Event Unbind throws exception when unbinding last handler for given event.

[khoipham]

When unbinding an event attached to a plain object, an exception is thrown when trying to remove generic event handler when if no more handlers exist.

Line 1772 calls >>

removeEvent( elem, type, elemData.handle );

removeEvent expects a DOM element, but plain object is passed instead.

[khoipham]

QUnit test

[john]

Duplicate of #6184.