guest user can download "large" collections

[moritzschepp]

There is a setting defining the threshold for "large" collections. When these are downloaded, a zip file is generated asynchronously, once complete, the user gets an email with a download link.

This currently also works with the guest user (who doesn't have a valid email address in general).

The functionality should be disabled for the guest user.

Verify problem persists in v5.