Bug 851438 - crash [@ MozQWidget::showEvent] r=romaxa. DONTBUILD

widget/qt/mozqwidget.cpp

@@ -414,7 +414,9 @@ void MozQWidget::hideEvent(QHideEvent* aEvent)
 
 void MozQWidget::showEvent(QShowEvent* aEvent)
 {
+    if (mReceiver) {
         mReceiver->showEvent(aEvent);
+    }
     QGraphicsWidget::showEvent(aEvent);
 }