do not destroy FX-mixer-view when closing

git-svn-id: https://lmms.svn.sf.net/svnroot/lmms/trunk/lmms@982 0778d3d1-df1d-0410-868b-ea421aaaa00d

src/gui/fx_mixer_view.cpp

@@ -221,6 +221,7 @@ fxMixerView::fxMixerView() :
 
 	// add ourself to workspace
 	engine::getMainWindow()->workspace()->addSubWindow( this );
+	parentWidget()->setAttribute( Qt::WA_DeleteOnClose, FALSE );
 
 	// we want to receive dataChanged-signals in order to update
 	setModel( m );