With large-result sets we go OOM.
Ideally we should respect the requested properties,
but they are not exposed by Sabre DAV.

It's unclear whether there are clients that rely on fetching attachments
via calendar-query, but since there is no paging, it will in any case
fail for large enough collections.

Potential alternatives to this approach:

• Only disable fetching of attachments beyond a certain number of hits
• Fix the memory consumption instead. In principle we shouldn't be holding all objects in memory if we only return certain properties, but this may be a sabre issue.
• Find a way to detect which properties are requested, and only disable fetching of attachments if we don't need it to fullfill the request.