Fixed #1170 (Assertion when receiving updated SDP offer with all media lines removed):
 - pjsua_media.c checks if audio media is present in the offer; if not, do not set any answer
 - sip_inv.c checks if app has supplied an answer after on_rx_offer() callback is called, and returnd 488 (Not Acceptable) if not (previously, it will return 200/OK without SDP!)
 - added a SIPp scenario file to reproduce this


git-svn-id: https://svn.pjsip.org/repos/pjproject/trunk@3383 74dad513-b988-da41-8d7b-12977e46ad98
3 files changed