Major Description
A negative inflight count can result from rollback redelivery as each rollback decremented the inflight count
With a 0 maxRedeliveryAttempts policy, the poisonAck was incrementing inflight.
poisinAck should manage the inflight as they are still present (inflight) in the consumer till they are acked via commit or a poisonAck.
adding some asserts to the existing DeadLetterTest junit demonstrates the problem.