s4:auth_winbind: fix error checking in winbind_check_password()

We need to handle every error instead of just NT_STATUS_NO_SUCH_USER,
the callers also doesn't require NT_STATUS_NOT_IMPLEMENTED anymore.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
