Cloned from: https://pagure.io/freeipa/issue/9535

The PAC generator structure [`ipadb_context.mspac`](https://pagure.io/freeipa/blob/ipa-4-11/f/daemons/ipa-kdb/ipa_kdb.h#_153) is allocated systematically and its content is not guaranteed to be exhaustive.

In some cases, the behavior of the KDB plugin must change depending of the capacity of the domain to generate PACs. But the current implementation makes this difficult to determine.

The `ipadb_context.mspac` structure should be set only if all its attributes can be set, or set to NULL otherwise.