LDAP Recursion broken

Took me a while to track this down, but it appears a minor tweak to the ldap recursion broke logins for anyone in a nested group, not in the base group.

Had to add the [0] back in and everything went back to working.

Against 2019 Domain Controllers, though I'm not sure that matters here as it wouldn't work against older DCs either.

root@observium:/data/observium/html/includes/authentication# diff ldap.inc.php ldap.inc.php.def
83c83
< $result = ldap_search_user($element[$config['auth_ldap_attr']['dn']][0], $userdn, $depth);
—
> $result = ldap_search_user($element[$config['auth_ldap_attr']['dn']], $userdn, $depth);