chg: dev: Catch rare named crash in recursive resolution earlier for diagnosis

A rare crash has been observed in named while it is resolving upstream nameserver
addresses for a recursive query, surfacing as a segmentation fault with no immediate
clue as to the cause. This change adds internal consistency checks so that a future
occurrence of the same condition aborts named with a diagnostic message at the point
the inconsistency arises, rather than corrupting state and crashing later in
an unrelated location.

Closes #5602

Merge branch '5602-adb-find-sanity-checks' into 'main'

See merge request isc-projects/bind9!11943