Update based on comments.
Update based on comments.

- Simplify the check for closing message channel.
- When resending subscriptions, unsubscribe if adjustedMax is at 0.

wallyqs/go-nats,wallyqs/go-nats,ZebinKang/go-nats,apcera/nats,ZebinKang/go-nats,nats-io/go-nats,pires/nats,pires/nats,nats-io/go-nats,apcera/nats,nats-io/nats,nats-io/nats