Fix a bug in catz_process_apl()

Fix a bug in catz_process_apl()

The allow-transfer/allow-query catalog zone custom properties support
only APL RRtypes. All other types are correctly rejected by the
catz_process_apl() function. However, when an APL RRtype is processed
by that function, and another (non-APL) RRtype is then attempted to be
processed, there is an assertion failure happening in the prologue
of the function because `*aclbp != NULL` (i.e. an APL has been already
processed). Move the code to do type checking before the affected
REQUIRE assertion.

(cherry picked from commit 67e0090371b4bd4c8933b8644f68a3dbc592a214)