Give a 200 response for valid user pages

Rather than sending a 404 on empty user pages, send a 200 response.
It's ideal to use the user's page as an OpenID identity url, but
OpenID expects 200 responses on identity urls. If we send 404s on
empty user pages it's necessary for all users to have content on
their pages to use Wikimedia as a provider. This change eliminates
that requirement.

Fixes: bug 45241
Change-Id: I527aa9d9c19c5cef7bebde78ef22f426bcbb3cd6
Merge "Give a 200 response for valid user pages"