consumer: v0.14.0 implementation can lead to unprocessable messages

[gnuletik]

While reviewing the code of v0.14.0, I realized that the consumer returns NackRequeue automatically if a mutex is locked.

https://github.com/wagslane/go-rabbitmq/blob/ef6a38050e8e093ad2e0aad5e1f7e37e593548c2/consume.go#L96-L98

However, I'm concerned that when using a policy with a delivery-limit, this will lead to messages landing in a DLQ "silently" (without any error on the consumer side).

WDYT of removing this automatic NackRequeue and wait for the mutex instead?

Thanks!