fix: check if the channel is closed before returning ws.result to prevent panic

[mhughdo]

Overview

• If sub.Unsubscribe() func is not called properly, it could cause panic:
  panic: interface conversion: ws.result is nil, not *ws.LogResult

• It's due to Recv() receiving values from the closed channel. I think it's better to handle this case instead of letting it panic.

Changes

• Checking if the channel is closed before returning the value.

[gagliardetto]

thank you!