I prepared this patch as a part of [1]. I provided the reported a gdb
script to help localize the code where we mess up with hostid data, but
the reporter does not see the issue any more, thus I'm sending the
patch separately.
It is definitely not a solution for #1751, but at least sssd will not
crash. Similar check is also present in other be handlers.
[1]
https://fedorahosted.org/sssd/ticket/1751