<rdar://problem/5271774> REGRESSION: A crash occurs when closing a window that contains a QT movie
        
        In some cases, calling [super dealloc] might end up calling visibleRect, so make sure to
        set _element to 0 so we won't send a message to a freed object and crash.
        
        * Plugins/WebKitPluginContainerView.mm:
        (-[WebKitPluginContainerView dealloc]):
        (-[WebKitPluginContainerView visibleRect]):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@23552 268f45cc-cd09-0410-ab3c-d52691b4dbfc