nsswitch: Fix wbcListUsers test
With an AD DC, wbcListUsers returns the users in the DOMAIN SEPARATOR
USERNAME format. The test then calls wbcLookupName with the domain name
and the previous string (including domain and separator) as username.
Fix this by passing the correct username and adding some additional
checks.
BUG: https://bugzilla.samba.org/show_bug.cgi?id=13312
Signed-off-by: Christof Schmitt <cs@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
(cherry picked from commit
3c146be404affc894c0c702bbfbfcc4fb9ed902b)