[OWL-935] fix crash while sending data to multiple transfer
[OWL-935] fix crash while sending data to multiple transfer

reference here.
https://github.com/open-falcon/agent/pull/46/files

masato25/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend,masato25/open-falcon-backend,Cepave/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend