fix: usr: Fix rndc modzone behavior for a zone in named.conf

If a zone was present in the configuration file and not originally added by `rndc addzone`, `rndc modzone` for that zone would succeed once but subsequent `modzone` attempts would fail. This has been fixed.

Closes #5826

Merge branch '5826-fix-subsequenrt-rndc-modzone' into 'main'

See merge request isc-projects/bind9!11744