Incorrect login redirect in some rare cases

[joemull]

Problem

I was working on #3899 and realised that this function has a bug, though I don't think this code is ever run because we don't pass a string as login_redirect:

https://github.com/BirkbeckCTP/janeway/blob/4218c13fc3b8b6d453b8fc5b4e946f0ea2362c69/src/security/decorators.py#L48-L50

Line 49 should have login_redirect, probably?

To reproduce

1. In dev, set login_redirect to a string inside base_check.
2. Log out and try to access the manager page.
3. Inspect the URL.

Here's the pdb output:

> /home/joe/git/janepr/src/security/decorators.py(51)base_check()
-> params = urlencode({"next": redirect})
(Pdb) n
> /home/joe/git/janepr/src/security/decorators.py(52)base_check()
-> return redirect('{0}?{1}'.format(reverse('core_login'), params))
(Pdb) params
'next=%3Cfunction+redirect+at+0x7ff153f1b010%3E'