[dev] Functions folder doesn’t get served if initially empty

[kripod]

- Do you want to request a feature or report a bug?

I would like to report a bug.

- What is the current behavior?

When running netlify dev with build.functions in netlify.toml pointing to a non-existing folder, functions generated in watch mode aren’t served via HTTP.

Reproduction: Run yarn netlify dev (instead of yarn develop) in the root of kripod/exigo

- What is the expected behavior?

Functions generated on the fly should be available in development mode.

[sarahetter]

Closing as stale. Please re-open if needed