Fix the infinite recursion problem reported in
We can't solely rely on the port in the URI to determine whether we will be
recursively called by decode_tcp_ports(). Instead also check the conversation
entry too: if we find that we are the subdissector for this conversation
(which we might be--without the port being in our list of ports--if we
heuristically picked up the conversation or the user did Decode-As),
just bail out and dissect the payload as data.