We set the `kStartedReading` flag from `_read()` for Worker stdio,
and then `ref()` the port.
However, the `.on('end')` handler is also attached when `._read()`
is not called, e.g. when `process.stdin` inside a Worker is prematurely
ended because stdin was not enabled by the parent thread.
In that case, we should not call `.unref()` for stdin if we did not
also call `.ref()` for it before.
Fixes: https://github.com/nodejs/node/issues/28144
PR-URL: https://github.com/nodejs/node/pull/28153
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
