QT4: set rowUniformHeights to true on playlistview

according to doc, thisway view should be able to do some optimisation
over itself, and I didn't figure out anycase that rows wouldn't be same
height on playlist.

modules/gui/qt4/components/playlist/standardpanel.cpp

@@ -71,6 +71,7 @@ StandardPLPanel::StandardPLPanel( PlaylistWidget *_parent,
     view->setAcceptDrops( true );
     view->setDropIndicatorShown( true );
     view->header()->setSortIndicator( -1 , Qt::AscendingOrder );
+    view->setUniformRowHeights( true );
     view->setSortingEnabled( true );