Don't show AFT if user is both logged out and on action=purge,
because in that scenario there is no article being shown (instead, in such scenario the user sees a form with a button to clear the cache, which is then redirected back to the article (action=view).
This bug was fairly rare though, since the MediaWiki interface doesn't contain any links to action=purge for logged-out users (or even logged-in users for that matter), but some gadgets and templates do link to it.
Resolves
bug 30100 - Hide AFT for anonymous users on purge action.