This fixes bug #GH76 where an exception like
```
Reverse for 'defender_unblock_username_view' with arguments '(u'user+test@domain.tld',)' and keyword arguments '{}' not found. 1 pattern(s) tried: [u'admin/defender/blocks/username/(?P[A-Za-z0-9-._@]+)/unblock$']
```
was raised when trying to access the `/admin/defender/blocks/` URL when a user with a plus sign had been locked out.