DNS: WKS RR Protocol field is read as 4 bytes instead of 1

In the attached pcap file, there's a single DNS packet with WKS RR in the Prerequisites section.
The Protocol field of this RR is read as if it is 4 bytes long instead of 1, which actually reads part of the bytes of the following RR.

Found by boaz

Bug:10675
Change-Id: Icf12c7f3864b629a242598373c06eee4de0ca098
Reviewed-on: https://code.wireshark.org/review/5170
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>
(cherry picked from commit aec5ffb535be189a0861531aeceb7be557e47336)
Reviewed-on: https://code.wireshark.org/review/5173
Reviewed-by: Michael Mann <mmann78@netscape.net>