previously we would retry if the task was queued up for retry but the
status is in "received-ack" or "received-err". We don't expect that a
task will be retried after getting this status, but if there are
duplicate tasks that could happen. Lets plan for the worst by saying
"only process a retry if the task is currently in sending".
this way, if a duplicate task is on retry and the first task goes
through succesfully, the duplicate task will give up.