Global Drop {{ referer }} renders nothing when used in conjunction with {% authorize %}

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Steps to reproduce this issue:

1. Set up a site with Authorization, e.g. https://github.com/locomotivecms/site-templates/tree/master/auth.
2. Set up a page with {% authorize 'accounts', 'login' %}.
3. Set up login.liquid (with handle: login) and include {{ referer }}.
4. Deploy the site.
5. Without being authenticated, navigate to the page created in step 2 ({% authorize %} will redirect you to the login page).
6. Observe that {{ referer }} renders nothing.