IPA: handle searches by SID in apply_subdomain_homedir
https://fedorahosted.org/sssd/ticket/2391
apply_subdomain_homedir() didn't handle the situation where an entity
that doesn't match was requested from the cache. For user and group
lookups this wasn't a problem because the negative match was caught
sooner.
But SID lookups can match either user or group. When a group SID was
requested, the preceding LDAP request matched the SID and stored the
group in the cache. Then apply_subdomain_homedir() only tried to search
user by SID, didn't find the entry and accessed a NULL pointer.
A simple reproducer is:
$ python
>>> import pysss_nss_idmap
>>> pysss_nss_idmap.getnamebysid(group_sid)
The group_sid can be anything, including Domain Users (XXX-513)
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>