prevent div by zero

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@13179 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/switch_rtp.c

@@ -1500,7 +1500,7 @@ static int rtp_common_read(switch_rtp_t *rtp_session, switch_payload_t *payload_
 			}
 
 			poll_loop = 1;
-			rtp_session->missed_count += (poll_sec * 1000 ) / (rtp_session->ms_per_packet / 1000);
+			rtp_session->missed_count += (poll_sec * 1000 ) / (rtp_session->ms_per_packet ? rtp_session->ms_per_packet : 20 / 1000);
 			bytes = 0;
 		}