SDAP: do not fail if refs are found but not processed
It is possible to end up with not-processed referrals when
using AD provider and ldap_referrals=true.
Resolves:
https://fedorahosted.org/sssd/ticket/2906
Reviewed-by: Stephen Gallagher <sgallagh@redhat.com>
(cherry picked from commit 468495d91d536603a1c485424275b6dcf2bb83de)