sdp: in media_decode() reset rdir if port is zero

Consider the case e.g. in Session Progress SDP when the port number is zero!
This, means that the media should be deactivated and no attribute lines will
follow in the SDP. In this case the rdir should be set to SDP_INACTIVE.

src/sdp/msg.c

@@ -222,6 +222,9 @@ static int media_decode(struct sdp_media **mp, struct sdp_session *sess,
 
 	m->rdir = sess->rdir;
 
+	if (!pl_u32(&port))
+		m->rdir = SDP_INACTIVE;
+
 	*mp = m;
 
 	return 0;