Updates to transaction reassembly, from Ronnie Sahlberg.

Updates to transaction reassembly, from Ronnie Sahlberg.

Add some checks for null tvbuff arguments.

When dissecting transaction setup, parameters, and data when we couldn't
dissect it as a pipe or mailslot transaction, use the reported length of
the supplied tvbuff, not the actual length, as the amount of data
present.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@4291 f5534014-38df-0310-8fa8-9805f1628bb7