Fixes T12035. Normally, the "abc" -> "abc/" redirect is handled automatically when "abc" hits a 404.
However, in this case, "source/x" does not 404. We route this to a valid controller because some VCS requests omit the slashes, then manually perform the redirect if we aren't serving a VCS request.
Allow this controller to serve public resources so we can serve the redirect to logged-out users instead of prompting them to login so they can be redirected.