Fix NPE and MediaRelay on incorrect SDP
Fix NPE and MediaRelay on incorrect SDP

BelledonneCommunications/flexisip,gale320/flexisip,BelledonneCommunications/flexisip,BelledonneCommunications/flexisip,gale320/flexisip,BelledonneCommunications/flexisip,biddyweb/flexisip,gale320/flexisip,gale320/flexisip,biddyweb/flexisip,biddyweb/flexisip,biddyweb/flexisip