rhbz#782736 use right device for converting size

Change-Id: If433376df24a3646d80f30e1dfa45463653ea72b

forms/source/richtext/richtextcontrol.cxx

@@ -401,7 +401,7 @@ namespace frm
         ::Size aSize = pControl->GetSizePixel();
         const MapUnit eTargetUnit = pTargetDevice->GetMapMode().GetMapUnit();
         if ( eTargetUnit != MAP_PIXEL )
-            aSize = pControl->PixelToLogic( aSize, eTargetUnit );
+            aSize = pTargetDevice->PixelToLogic( aSize );
 
         ::Point aPos( _nX, _nY );
         // the XView::draw API talks about pixels, always ...