fs: fix error handling

Right now there are multiple cases where the validated entry would
not be returned or a wrong error is thrown. This fixes both cases.

PR-URL: https://github.com/nodejs/node/pull/19445


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>