We still need to figure out how a bad header is getting into the
outgoing message but this patch to pjproject prevents attempting
to print that header and causing a crash.
For several users, this crash happens when sending 183 progress
messages.
ASTERISK-26832
Reported by: Ross Beer, Jan Rozhon
Change-Id: Ie5c5a921c890c843587763e7f33f987dfe66bd16