worker: allow execArgv and eval in combination

It was likely an oversight that `execArgv` was only read when
no filename/URL was provided.

PR-URL: https://github.com/nodejs/node/pull/26533


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>