Conpherence - fix a bug

Summary: gotta idx() on this as the user may have no conpherences at all.

Test Plan: loaded up my 'noconpherences' user and observed no errors in the error log. my normal test user still worked okay too.

Reviewers: epriestley, garoevans

Reviewed By: garoevans

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5791