Navbar missing in admin group edit page

### Steps to reproduce

1. Log in to Hypothesis as an administrator
2. Go to the details view for an existing group in the admin pages (at `/admin/groups/{id}`, eg. https://hypothes.is/admin/groups/__world__)

### Expected behaviour
Navbar is visible at top of page

### Actual behaviour
Navbar is present but contains no links:

### Additional details

The navbar rendering logic omits links if the user does not have permission to use a particular section of the admin pages. My initial guess is that the [`request.has_permission` check](https://github.com/hypothesis/h/blob/9b1b6cd34fc931d7f1e2807a9484f9afbbcb2810/h/templates/layouts/admin.html.jinja2#L57) is incorrectly failing for all of these links.