I am chasing a Shenandoah + CDS bootstrapping problem, where Shenandoah tries to insert the filler at the time when Universe is not yet initialized. It currently fails rather cryptically on attempt to store `null` class. We could really use an assert on accessing various Klass definitions in Universe.

We already do this for TypeArrayKlass-es, so this change would cover fillerArrayKlass and objectArrayKlass.