DNS NXT RR is parsed incorrectly

The queries RRs and answers RRs are parsed fine.
However, only the first 2 authoritative RRs are parsed and none of the 3 additional RRs are parsed.
The second authoritative RR is of type NXT, and even though it has data length of 9, Wireshark reads all the bytes until the end of the packet as if they are part of bitmap in this RR (it reads 317 bytes too many).
This causes it to not parse the rest of the RRs correctly.

Found by boaz

Bug:10615
Change-Id: I22e5987c44a11399b07c3106fbb70c6e9e867afe
Reviewed-on: https://code.wireshark.org/review/4940
Reviewed-by: Michael Mann <mmann78@netscape.net>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>