Caused/introduced by JDK-8262068 .

Fixed later as a byproduct of JDK-8210708 in JDK 20.

Symptom: We crash with -UseClassUnloading when dumping dead objects in non-collected (since JDK-8210708) regions. Those dead objects contain references to other dead objects that did live in collected regions (either as members or as array elems). When trying to dump those object references, we crash when extracting the Klass* from these dead references. Typically in DumperSupport::mask_dormant_archived_object(oopDesc*).

This seems to be exactly the bug fixed by JDK-8265259, but JDK-8265259 limits the fix to +ClassUnloading. But one can have cycles of dead objects without their classes being unloaded. I think that happens here.