fix: usr: Fix a serve-stale issue with a delegated zone

When ``stale-answer-client-timeout 0`` option was enabled, it could be ignored
when resolving a zone which is a delegation of an authoritative zone belonging
to the resolver. This has been fixed.

Closes #5275

Merge branch '5275-stale-answer-client-timeout-0-and-delegation-fix' into 'main'

See merge request isc-projects/bind9!10381