fix: dev: Fix a possible crash when cleaning up a view's caches

In rare cases named could crash while a view was being removed, for example
during reconfiguration or shutdown, as its internal caches were torn down.
This has been fixed.

Closes #6119

Merge branch '6119-fix-possible-uaf-when-destroying-dns_badcache' into 'main'

See merge request isc-projects/bind9!12177