res_pjsip_session: Fixed wrong session termination

res_pjsip_session: Fixed wrong session termination

When the Asterisk receives 200 OK with invalid SDP,
the Asterisk/PJPROJECT terminating the session.
But if the channel was in the Bridge, Asterisk tries send
the Re-Invite before terminating the session.
And when the Asterisk sending the Re-Invite, it doesn't check
the SDP is NULL or not. This crashes the Asterisk.

Fixed it to close the session correctly if the UAS sends the
200 OK with wrong SDP.

ASTERISK-28743

Change-Id: Ifa864e0e125b1a7ed2f3abd4164187e1dddc56da