Fix a bad call when prefilling ApplicationSearch from ?projects=some_slug

Summary: Fixes T10299.

Test Plan:
  - Visited `/maniphest/?projects=x` locally, where `x` is some valid project slug.
  - Before patch: Fatal on `requireViewer()` call.
  - After patch: Works correctly, filling the correct project into parameters.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10299

Differential Revision: https://secure.phabricator.com/D15214

src/applications/project/searchfield/PhabricatorProjectSearchField.php

@@ -34,7 +34,7 @@ final class PhabricatorProjectSearchField
 
     if ($slugs) {
       $projects = id(new PhabricatorProjectQuery())
-        ->setViewer($this->requireViewer())
+        ->setViewer($this->getViewer())
         ->withSlugs($slugs)
         ->execute();
       foreach ($projects as $project) {