issue: ACL Oopsie

This addresses an issue where initially saving the ACL will fail. This is
due to the incorrect variable being used to lookup the IP in the ACL. This
updates the variable from `$acl` to the correct variable `$vars['acl']`.

include/class.config.php

@@ -1188,7 +1188,7 @@ class OsticketConfig extends Config {
             // Check if Admin's IP is in the list, if not, return error
             // to avoid locking self out
             if (!in_array($vars['acl_backend'], array(0,2))) {
-                $acl = explode(',', str_replace(' ', '', $acl));
+                $acl = explode(',', str_replace(' ', '', $vars['acl']));
                 if (!in_array(osTicket::get_client_ip(), $acl))
                     $errors['acl'] = __('Cowardly refusing to lock out active administrator');
             }