[9.20] fix: usr: Fix a statistics channel counter bug when 'forward only' zones are...

[9.20] fix: usr: Fix a statistics channel counter bug when 'forward only' zones are used

When resolving a zone with a 'forward only' policy, and
finding out that all the forwarders are marked as "bad",
the 'ServerQuota' counter of the statistics channel was
incorrectly increased. This has been fixed.

Closes #1793

Backport of MR !9493

Merge branch 'backport-1793-serverquota-counter-bug-with-forward-only-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!9502