Ensure pvt is not NULL before dereferencing it.

(closes issue #14784)
 Reported by: pj


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@187674 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -5803,7 +5803,7 @@ static int sip_hangup(struct ast_channel *ast)
 				if (bridge) {
 					struct sip_pvt *q = bridge->tech_pvt;
 
-					if (IS_SIP_TECH(bridge->tech) && q) {
+					if (IS_SIP_TECH(bridge->tech) && q && q->rtp) {
 						ast_rtp_instance_set_stats_vars(bridge, q->rtp);
 					}
 				}
@@ -20656,7 +20656,7 @@ static int handle_request_bye(struct sip_pvt *p, struct sip_request *req)
 		if (bridge) {
 			struct sip_pvt *q = bridge->tech_pvt;
 
-			if (IS_SIP_TECH(bridge->tech) && q->rtp) {
+			if (IS_SIP_TECH(bridge->tech) && q && q->rtp) {
 				ast_rtp_instance_set_stats_vars(bridge, q->rtp);
 			}
 		}