Going to settings page of a repo you aren't admin does give proper 404 page

Using the latest version of 1.10+dev on try.gitea.io, if you go to https://try.gitea.io/richmahn/test/settings/collaboration as a user that doesn't have access to the repo, you get this error:

```template: repo/header:35:51: executing "repo/header" at <$.UnitTypeCode>: invalid value; expected models.UnitType```

instead of a 404 page.