wrong group quota calculations

I get a lot of warnings in my cron.log in Debian 10:

PHP Warning: A non-numeric value encountered in /usr/local/ispconfig/server/lib/classes/cron.d/100-monitor_hd_quota.inc.php on line 115

Its because all of the key indexes are off by one for the group calculation part at https://git.ispconfig.org/ispconfig/ispconfig3/-/blob/develop/server/lib/classes/cron.d/100-monitor_hd_quota.inc.php#L115. Its getting the "--" column instead of the next number based columns.

the lines causing the issue look like this:

$groupname = $s[0];
...
$data['group'][$groupname]['used'] += $s[1];
$data['group'][$groupname]['soft'] += $s[2];
$data['group'][$groupname]['hard'] += $s[3];

repquota -ag

Gruppe          belegt  weich   hart  Gnade   belegt weich hart  Gnade
----------------------------------------------------------------------
client1   --     384       0       0             64     0     0
client2   -- 2556584       0       0         105155     0     0
client3   --   68120       0       0           2797     0     0