add a check before a cast

vcl/unx/kde4/KDESalGraphics.cxx

@@ -369,6 +369,7 @@ sal_Bool KDESalGraphics::drawNativeControl( ControlType type, ControlPart part,
             // paints the whole menu item, so translate position (and it'll be clipped);
             // it is also necessary to fill the background transparently first, as this
             // is painted after menuitem highlight, otherwise there would be a grey area
+            assert( value.getType() == CTRL_MENU_POPUP );
             const MenupopupValue* menuVal = static_cast<const MenupopupValue*>(&value);
             QRect menuItemRect( region2QRect( menuVal->maItemRect ));
             QRect rect( menuItemRect.topLeft() - widgetRect.topLeft(),