Fix fatal in Conpherence NUX state

Summary: Fixes T12619.

Test Plan: Faked `return array()` in ConpherneceThreadQuery, got a NUX instead of fatal.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12619

Differential Revision: https://secure.phabricator.com/D17764

src/applications/conpherence/controller/ConpherenceListController.php

@@ -89,13 +89,14 @@ final class ConpherenceListController extends ConpherenceController {
       default:
         $data = $this->loadDefaultParticipation($limit);
         $all_participation = $data['all_participation'];
-
+        if ($all_participation) {
           $conpherence_id = head($all_participation)->getConpherencePHID();
           $conpherence = id(new ConpherenceThreadQuery())
             ->setViewer($user)
             ->withPHIDs(array($conpherence_id))
             ->needProfileImage(true)
             ->executeOne();
+        }
         // If $conpherence is null, NUX state will render
         break;
     }