resolved: if dns_packet_append_answer() fails count how many RRs were successfully...

resolved: if dns_packet_append_answer() fails count how many RRs were successfully added

This is useful later when handling the truncation case: if we can't add
all RRs we'd like to add we need to set the TC bit, but still report the
number of RRs we added (and not the number of RRs we would have liked to
add) to the packet.