CVE-2012-6150: Fail authentication for single group name which cannot be converted...

CVE-2012-6150: Fail authentication for single group name which cannot be converted to sid

furthermore if more than one name is supplied and no sid is converted
then also fail.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=10300
Bug: https://bugzilla.samba.org/show_bug.cgi?id=10306

Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: David Disseldorp <ddiss@samba.org>
[ddiss@samba.org: fixed incorrect bugzilla tag I added to master commit]