(stable) Add sound to logged out Conpherence

Summary: Fixes T12735. Adds a sound if the user is logged out, skips checking a setting.

Test Plan: set participants to null and verify sound plays, no exceptions1111

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12735

Differential Revision: https://secure.phabricator.com/D17973