Fix query for participants by notification level
Fix query for participants by notification level

The sessions were left joined to the attendees, so all the attendees in
the conversation that were not active were not included in the result.

Signed-off-by: Daniel Calviño Sánchez <bd7629e975cc0e00ea7cda4ab6a120f2ee42ac1b@gmail.com>

nextcloud/spreed,nextcloud/spreed,nextcloud/spreed