#20 180 with Content-Type application/sdp but no content

[yohannmartineau]

if a 180 with Content-Type application/sdp is sent to peers, but no content is provided, while clicking hangup on peers, no BYE is sent.

see attached sipp script.

if Content-Type is removed, BYE is sent while clicking hangup.

[yohannmartineau]