Fix a logic error in cache_name()

Fix a logic error in cache_name()

A change in 6aba56ae8 (checking whether a rejected RRset was identical
to the data it would have replaced, so that we could still cache a
signature) inadvertently introduced cases where processing of a
response would continue when previously it would have been skipped.

(cherry picked from commit d0fd9cbe3b0455d0db04b5afe67b7edc44e55965)