Mailbox quota used space and used percentage sorting broken

short description

Email > Mailbox quota > Sort by Used space and Used % shows empty list

correct behaviour

Should show the quotas sorted as chosen

environment

Server OS: Ubuntu 16.04.6
Server OS version: xenial ISPConfig version: 3.1.15p2

PHP 7.0.33-0ubuntu0.16.04.6 (cli) ( NTS ) Copyright (c) 1997-2017 The PHP Group Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies with Zend OPcache v7.0.33-0ubuntu0.16.04.6, Copyright (c) 1999-2017, by Zend Technologies