src,fs: remove `ToLocalChecked()` call from `fs::AfterMkdirp()`

This merges the `IsEmpty()` call and the `ToLocalChecked()` call into a
single `ToLocal()` call.

Signed-off-by: Darshan Sen <darshan.sen@postman.com>

PR-URL: https://github.com/nodejs/node/pull/40386


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>