Do not highlight when drag and drop

source/app/plaYUVerApp.cpp

@@ -862,7 +862,7 @@ Void plaYUVerApp::updatePixelValueStatusBar( const QPoint & pos, PlaYUVerFrame*
 Void plaYUVerApp::dragEnterEvent( QDragEnterEvent *event )
 {
   //setText(tr("<drop content>"));
-  setBackgroundRole( QPalette::Highlight );
+  mdiArea->setBackgroundRole( QPalette::Highlight );
   event->acceptProposedAction();
 }