PR: https://github.com/wikimedia/CopyPatrol/pull/50

This only checks if they are blocked on the wiki they're trying to patrol. If you are blocked, this is what you'll see:

The "blocked" link goes to the block entry on the wiki. That way they can see why they were blocked, in the rare event they weren't already aware they were blocked.

Blocked users can still browse the leaderboard, and switch to other projects (assuming you aren't block on those either).

If you already had CopyPatrol open and you become blocked, and attempt to do a review, it will refresh the page, which will then show the above error.

I did not account for global locks, but if you can't login than I guess you can't use OAuth. There might be a similar issue where you already have CopyPatrol open, then you become globally locked and are still able to do reviews... but I'm going to guess the global lock will invalidate the OAuth session. This is difficult to test because I don't have rights to lock/unlock my test account, and I don't want to bother the stewards :/