Fix offset maybe lost problem.

[aftersss]

If two clients commit offset at the same time(the same topic and group, but different queueId), one of the queue's offset maybe lost.

[coveralls]

Coverage increased (+0.06%) to 50.55% when pulling bf459e5 on aftersss:master_fix_offset_maybe_loss into 63f18c9 on apache:develop.

[xiangwangcheng]

Thanks for your contribution!
The code LGTM.
But could u please change the destination branch to develop add some unit test to increase the coverage?

[aftersss]

Thanks for your contribution!
The code LGTM.
But could u please change the destination branch to develop add some unit test to increase the coverage?

Done.