Qt : Fix the way playlist columns are saved

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit 9a4af551)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

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

@@ -104,6 +104,7 @@ PLModel::PLModel( playlist_t *_p_playlist,  /* THEPL */
 
 PLModel::~PLModel()
 {
+    if(i_depth == -1)
         getSettings()->setValue( "qt-pl-showflags", rootItem->i_showflags );
     delCallbacks();
     delete rootItem;