blackbox: Sanitize items read from the blackbox header (#438)
blackbox: Sanitize items read from the blackbox header (#438)

covscan complained we don't check the blackbox header when
reading it in. (quite reasonably)

Note that we still get a covscan error for ->shared_data, but that's
really impossible to verify in the read routine, so I'll leave the
covscan waiver to handle that.
ClusterLabs/libqb,ClusterLabs/libqb,ClusterLabs/libqb