macosx: Try to clean a bit the prefs code.

modules/gui/macosx/prefs.m

@@ -363,9 +363,10 @@ static VLCTreeItem *o_root_item = nil;
                     default:
                         break;
                 }
-                vlc_object_release( (vlc_object_t *)p_main_module );
             }
 
+            vlc_object_release( (vlc_object_t *)p_main_module );
+
             /* List the modules */
             p_list = vlc_list_find( p_intf, VLC_OBJECT_MODULE, FIND_ANYWHERE );
             if( !p_list ) return nil;
@@ -584,7 +585,7 @@ static VLCTreeItem *o_root_item = nil;
         else
         {
             p_main_module = module_GetMainModule( p_intf );
-            assert( !p_main_module );
+            assert( p_main_module );
             module_config_t *p_items;
 
             unsigned int i, confsize;