tree a1261b642d44b48857a6123d13ef1bc2fe97b4de
parent 0296890a9136a0921da19442cf713a4ebb31f9b0
author hrsakai <hsakai@yahoo-corp.jp> 1607762865 +0900
committer GitHub <noreply@github.com> 1607762865 +0800
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Fix discard unacked messages (#413)

https://github.com/apache/pulsar-client-go/issues/389#issuecomment-741560624


### Motivation
When a consumer whose receive queue is not empty reconnects to a broker, unacked messages don't be redelivered to a client application and these are removed from backlog.
This is because StartMessageID is updated and the consumer implicitly acks redelivered unacked messages.
https://github.com/apache/pulsar-client-go/blob/v0.3.0/pulsar/consumer_partition.go#L972-L976
https://github.com/apache/pulsar-client-go/blob/v0.3.0/pulsar/consumer_partition.go#L507-L510



### Modifications
* If startMessageID is undefined, it will not be updated in order to prevent  unacked messages from being discarded by following logic.
.https://github.com/apache/pulsar-client-go/blob/v0.3.0/pulsar/consumer_partition.go#L507-L510