CqlClientConnection.Close() blocked forever

[joao-r-reis]

I believe this issue is a bit different from #36 and #38 because the blocked channel here is not the same as #38 .
Close() sets outgoing channel to nil and in the outgoingLoop if the channel becomes nil just before the loop tries to read from that channel, it will be blocked forever.

There's a check to see if the connection is closed just before that read but there's no locking involved so I believe this issue can occur. I saw this happen in a Github Action so I couldn't see exactly where the goroutines were blocked but looking at the logs I believe this is what happened.

[adutra]

Yes this looks different. It would be good to tackle #50 so that we can better isolate all the race issues in the client package.