src: fulfill Maybe contract in InlineDecoder

Use an empty/nothing `Maybe<>` to indicate a pending exception.

PR-URL: https://github.com/nodejs/node/pull/25140


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>