If "guest" user groups is disabled but it has GUI access, Zabbxi login page still has "sign in as guest" button.

Steps to reproduce:

1. Make sure "guest" user is on "guest" user group only.
2. Make "guest" user group disabled but allow GUI access.
3. Sign out.

Result:
"Sign in as guest" button is shown. User still cannot sign in since guest group is disabled.