refine code, donot response call when transaction id is zero.

trunk/src/app/srs_app_rtmp_conn.cpp

@@ -922,7 +922,9 @@ int SrsRtmpConn::process_play_control_msg(SrsConsumer* consumer, SrsMessage* msg
     // @see https://github.com/winlinvip/simple-rtmp-server/issues/106
     // TODO: FIXME: response in right way, or forward in edge mode.
     SrsCallPacket* call = dynamic_cast<SrsCallPacket*>(pkt);
-    if (call) {
+    // only response it when transaction id not zero,
+    // for the zero means donot need response.
+    if (call && call->transaction_id > 0) {
         SrsCallResPacket* res = new SrsCallResPacket(call->transaction_id);
         res->command_object = SrsAmf0Any::null();
         res->response = SrsAmf0Any::null();