Minor routing and status code issues

[Larivact]

• Gitea version (or commit ref): 1.7.0

Description

• While Internal Server Errors display 500 they return a 404 status code.
• Missing commits sometimes return a 500 instead of a 404 (seems to be fixed):
  https://try.gitea.io/lunny/wewe/commit/000000 returns 404
  https://try.gitea.io/lunny/wewe/commit/0000000 returns 500
• If there are no wiki pages, any wiki page returns a 200:
  https://try.gitea.io/lunny/wewe/wiki/doesnotexist
• Missing wiki pages should return a 404 instead of redirecting to the index:
  https://try.gitea.io/gittea/curl/wiki/doesnotexist
• Invalid issue / pull requests identifiers redirect to the first issue / pull request instead of returning a 404
  https://try.gitea.io/lunny/wewe/issues/doesnotexist
  https://try.gitea.io/lunny/wewe/pulls/doesnotexist
• /user/repo/commit/ and /user/repo/commits/ should probably redirect to the default branch.

[adelowo]

💯

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs during the next 2 weeks. Thank you for your contributions.

[lunny]

I think we can close this now. And I don't agree we should redirect /user/repo/commit/ to repository homepage.