Don't crash when rndc delzone encounters a catz member

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.

Closes #3745 (closed)