Visiting `/_error` in development causes non-stop reloading

[ijjk]

Bug report

Describe the bug

When you visit /_error in development the page reloads non-stop and the error page is rendered with a status of 200 and text of An unexpected error occurred.

To Reproduce

Steps to reproduce the behavior, please provide code snippets or a repository:

1. Create minimal Next.js project yarn create next-app error-loop
2. Visit /_error in your browser
3. See the error

Expected behavior

Still being discussed, most likely to render 404 similar to _app and _document

Screenshots

System information

• OS: [e.g. macOS, Windows] any
• Browser (if applies) [e.g. chrome, safari] any
• Version of Next.js: [e.g. 6.0.2] latest (9.0.2)

Additional context

Related PR here