The Vercel preset requires an index file

[Gbuomprisco]

In my Remix project - I have the following file structure:

_marketing._index
_marketing.blog
...
auth
auth.sign-in._index

Remix (without the Vercel preset) correctly infers that the index page should be (_marketing._index).

This is useful, as it allows us to create a layout around the marketing side of the website - and another one for auth, dashboard, etc.

However, the Vercel preset will return a 404 with the structure above.

To reproduce:

1. remove the _index.tsx file
2. add a pathless layout with a route _marketing._index/route.tsx