vcl: Implement drawing CTRL_MENUBAR and PART_MENU_ITEM on KDE

Currently, menubar's background is drawn in window's background color
and no menubar's specific background color. To fix this, The patch
calls QStyle::drawControl() with QStyle::CE_MenuBarEmptyArea.

Change-Id: I89b9decc016a926a0f00b9663ec1a5bce81daac1
Reviewed-on: https://gerrit.libreoffice.org/4025Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>

vcl/unx/kde4/KDESalGraphics.cxx

@@ -308,6 +308,9 @@ sal_Bool KDESalGraphics::drawNativeControl( ControlType type, ControlPart part,
         }
         else if (part == PART_ENTIRE_CONTROL)
         {
+            QStyleOptionMenuItem option;
+            draw( QStyle::CE_MenuBarEmptyArea, &option, m_image,
+                  vclStateValue2StateFlag(nControlState, value) );
         }
         else
         {