When anon is allow to upload files and a anon is visiting Special:UploadStash he get a error:

UploadStash::listFiles No user is logged in, files must belong to users

In my opinion it is better to add a message, that anon has no Stash and not throw a error with backtrace.

Thanks.

LocalSettings:
$wgGroupPermissions['*']['upload'] = true;

Version: 1.20.x
Severity: minor