Blocks VisualEditor while logged out

[mrsrec]

Not a super high-priority issue as the Scratch Wiki already disallows logged-out editing and there are no known other wikis using it, but it is still unintended behaviour.

Also, this extension does many of the same things that https://www.mediawiki.org/wiki/Extension:CrawlerProtection does - might be worth archiving this in the future in favour of that extension.