Title: #475: AD: Use the right sdap_domain for the forest root
Thanks for reporting the issue. I must have tested only with a client joined to a child
domain, because the crash was happening simply because the root domain attributes are
expected to be NULL and in that case we can just just `be_ctx->dom` as the domain.
See the full comment at https://github.com/SSSD/sssd/pull/475#issuecomment-363819017