Chunk server: do not update chunk checksum vector if chunk size is zero.
Chunk server: do not update chunk checksum vector if chunk size is zero.

thebigbrain/qfs,thebigbrain/qfs,quantcast/qfs,chanwit/qfs,chanwit/qfs,qnu/qfs,chanwit/qfs,quantcast/qfs,thebigbrain/qfs,fengshao0907/qfs,quantcast/qfs,fengshao0907/qfs,fengshao0907/qfs,quantcast/qfs,qnu/qfs,fengshao0907/qfs,thebigbrain/qfs,fengshao0907/qfs,fengshao0907/qfs,fengshao0907/qfs,chanwit/qfs,chanwit/qfs,thebigbrain/qfs,qnu/qfs,qnu/qfs,quantcast/qfs,chanwit/qfs,thebigbrain/qfs,qnu/qfs,qnu/qfs,quantcast/qfs,chanwit/qfs,thebigbrain/qfs,quantcast/qfs,qnu/qfs,chanwit/qfs,thebigbrain/qfs,qnu/qfs,fengshao0907/qfs,quantcast/qfs