Performance fix: Do not ask for folder attributes if we know that folder do not exists

program/steps/settings/folders.inc

@@ -291,10 +291,12 @@ function rcube_subscription_form($attrib)
             $classes[] = 'virtual';
         }
 
-        if (!$protected) {
+        // Check \Noselect flag (of existing folder)
+        if (!$protected && in_array($folder['id'], $a_unsubscribed)) {
                 $attrs = $STORAGE->folder_attributes($folder['id']);
                 $noselect = in_array('\\Noselect', $attrs);
             }
+        }
 
         $disabled = (($protected && $subscribed) || $noselect);