Fix potential seg (Bug #2550)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@3857 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_iax2.c

@@ -2628,8 +2628,10 @@ tackygoto:
 		cs[1] = cs[2];
 	}
 	lock_both(callno0, callno1);
-	iaxs[callno0]->bridgecallno = 0;
+	if(iaxs[callno0])
-	iaxs[callno1]->bridgecallno = 0;
+		iaxs[callno0]->bridgecallno = 0;
+	if(iaxs[callno1])
+		iaxs[callno1]->bridgecallno = 0;
 	unlock_both(callno0, callno1);
 	return res;
 }