Values longer than 128 bytes or with non-ASCII characters are rejected by
`StoreItemPart::from_str` with `ERR invalid_argument(...)`, but the
protocol did not say so.
Closes#319
A read timeout or an abrupt client hang-up unwound the channel thread,
which flooded the logs with "closing channel" panics and skipped the
connected clients counter decrement, leaking a client slot each time.
Fixes#256
upstream
dualfroz