Prerendering fails when custom serverDir and rollup.output.entryFileNames is used

[brandonroberts]

Environment

Node

Reproduction

https://stackblitz.com/edit/github-kk3ajf?file=nitro.config.ts

1. Run the StackBlitz
2. Stop the server
3. Run npm run build
4. Note the prerender fails with a file not found error
5. Comment out either the rollup.output.entryFilenames or the output.serverDir
6. Run npm run build
7. Note the prerender finishes successfully

Describe the bug

The prerenderer looks for an index.mjs when there is a custom entryFilenames set to a custom filename, such as server.mjs

Additional context

No response

Logs

No response