winbindd: Fix crash in cm_connect_sam()
Fix segv when talking to parent DC (joined to child domain).
The root cause was
(a) storing the parent domain in the cli_state struct caused
the NTLMSSP pipe bind to fail which made us fallover to
the schannel code path
(b) the dcinfo pointer in cm_get_schannel_dcinfo() was returning
NULL even though the function indicated success.
(cherry picked from commit
5ce4a2ae6697970ea37d0078a506615b4b7a9a9c)
(cherry picked from commit
72d138adc200ab36e324721900af1a06d0879318)