Quick hack to solve the save volume on exit.

This is of course NOT a good solution, and it has nothing to do in the interface...
So, either we let it like this, or we implement in the good place (not in intf)
or we remove this option

modules/gui/qt4/main_interface.cpp

@@ -249,6 +249,15 @@ MainInterface::~MainInterface()
 {
     msg_Dbg( p_intf, "Destroying the main interface" );
 
+    /* Saving volume */
+    if( config_GetInt( p_intf, "qt-autosave-volume" ) )
+    {
+        audio_volume_t i_volume;
+        aout_VolumeGet( p_intf, &i_volume );
+        config_PutInt( p_intf, "volume", i_volume );
+        config_SaveConfigFile( p_intf, NULL );
+    }
+
     if( playlistWidget )
     {
         if( !isDocked() )