fix crash in query_respond_any() from all records being hidden

fix crash in query_respond_any() from all records being hidden

in query_respond_any(), the assumption had previously been made that it
was impossible to get past iterating the node with a return value of
ISC_R_NOMORE but not have found any records, unless we were searching
for RRSIG or SIG. however, it is possible for other types to exist but
be hidden, such as when the zone is transitioning from insecure to
secure and DNSSEC types are encountered, and this situation could
trigger an assertion.  removed the assertion and reorganized the code.

(cherry picked from commit 3e74c7e5ffc455051549b1199328c76ddc5c72cc)