src: check for empty maybe local

Using ToLocalChecked on MaybeLocal without verifying it's empty
can lead to unattempted crash.

PR-URL: https://github.com/nodejs/node/pull/32339


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>