Don't fail with no image macros

Summary: .. IN (%Ls) with no file phids fails miserably.

Test Plan:
Went to /file/macro/ with and without patch. An exception is thrown
without it.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: 1063

src/applications/files/controller/macrolist/PhabricatorFileMacroListController.php

@@ -43,12 +43,16 @@ class PhabricatorFileMacroListController extends PhabricatorFileController {
     $pager->setURI($request->getRequestURI(), 'page');
 
     $file_phids = mpull($macros, 'getFilePHID');
+
+    $files = array();
+    if ($file_phids) {
       $files = id(new PhabricatorFile())->loadAllWhere(
         "phid IN (%Ls)",
         $file_phids);
       $author_phids = mpull($files, 'getAuthorPHID', 'getPHID');
       $handles = id(new PhabricatorObjectHandleData($author_phids))
         ->loadHandles();
+    }
 
     $rows = array();
     foreach ($macros as $macro) {