This bug was masked in the tests because the `catz` test script did an
`rndc addzone` before an `rndc delzone`. The `addzone` autovivified
the NZF config, so `delzone` worked OK.
This commit swaps the order of two sections of the `catz` test script
so that it uses `delzone` before `addzone`, which provokes a crash
when `delzone` requires a non-NULL NZF config.
To fix the crash, we now try to remove the zone from the NZF config
only if it was dynamically added but not by a catalog zone.
9fa20d6f6c