Fix resquery reference imbalance on TCP connect failure

Fix resquery reference imbalance on TCP connect failure

In fctx_query(), resquery_ref(query) is called before
dns_dispatch_connect() in anticipation of the resquery_connected()
callback consuming the reference.

When dns_dispatch_connect() fails synchronously on TCP (e.g. from
dns_transport_get_tlsctx() failing in tcp_dispatch_connect()), the
connect callback is never scheduled, so the extra reference is never
consumed.  The error path then tears down the query via manual cleanup
(isc_mem_put) without going through the refcount destructor, leaving
the reference imbalanced.

Fix by dropping the extra reference on the error path, just after
dns_dispatch_done() which cleans up the dispatch entry.