Staged users are emailed a link to visit topics in private categories they can't access

[cpradio]

This is a dup of

Some issues with staged users and their (in)ability to visit topics

Imagine an unknown user mailing to a category that has restricted access. One of the known users reply there, so the unknown user gets a notification by mail. In that mail there is the line that says Visit Topic or reply to this email to respond. But when visiting that topic, two things can happen: the forum is closed and the new user needs to login anyway the forum is not closed, but the user has no access to the category, because he’s not in that group For point 1, the new user should get …