Fix Pholio feed fatal

Summary: need to filter images that we can't find mocks for. Fixes T3645. Note I have some other errors in my feed which are really tricky to debug and might be garbage data; I want to see what happens in prod post this push.

Test Plan: set a mock visibility to no one and feed worked

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T3645

Differential Revision: https://secure.phabricator.com/D6631

src/applications/pholio/query/PholioImageQuery.php

@@ -138,8 +138,14 @@ final class PholioImageQuery
         ->execute();
       $mocks = mpull($mocks, null, 'getID');
     }
-    foreach ($images as $image) {
-      $image->attachMock($mocks[$image->getMockID()]);
+    foreach ($images as $index => $image) {
+      $mock = idx($mocks, $image->getMockID());
+      if ($mock) {
+        $image->attachMock($mock);
+      } else {
+        // mock is missing or we can't see it
+        unset($images[$index]);
+      }
     }
 
     return $images;