Don't dereference a pointer that may be NULL here.

Issue 10017.


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@71915 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/rtp.c

@@ -2525,6 +2525,9 @@ static int ast_rtcp_write(void *data)
 	struct ast_rtp *rtp = data;
 	int res;
 	
+	if (!rtp || !rtp->rtcp)
+		return 0;
+
 	if (rtp->txcount > rtp->rtcp->lastsrtxcount)
 		res = ast_rtcp_write_sr(data);
 	else