Attachments and links suggestions is not working

Note

Can be reproduced in the remote and embded setups.

I'm getting error 501 (Not Implemented) when calling http://localhost:9292/remote.php/dav with the SEARCH http action

Reproduction steps

1. create a few pages and upload a few attachments
2. create a new page and edit it
3. try to use the auto suggestion when adding an image or a link

Expected

The existing pages and attachments are proposed.

Actual

Nothing is ever suggested.