Exempt QNAME minimization queries from fetches-per-zone

Exempt QNAME minimization queries from fetches-per-zone

The calling fetch has already called fcount_incr() for this zone;
calling it again for a QMIN query results in double counting.

When resuming after a QMIN query is answered, however, we do now
ensure before continuing that the fetches-per-zone limit has not
been exceeded.