Diffusion - return 404 errors for bad URIs

Summary: Fixes T5646. Makes diffusion a much better user experience. Users now see a 404 exception page when they have a bad URI. Previously, they saw a developer-facing raw exception.

Test Plan: played around in diffusion a bunch. most of these changes were fairly mechanical at the end of the day.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T5646

Differential Revision: https://secure.phabricator.com/D11299

src/applications/diffusion/controller/DiffusionRepositoryListController.php

@@ -2,20 +2,13 @@
 
 final class DiffusionRepositoryListController extends DiffusionController {
 
-  private $queryKey;
-
   public function shouldAllowPublic() {
     return true;
   }
 
-  public function willProcessRequest(array $data) {
-    $this->queryKey = idx($data, 'queryKey');
-  }
-
-  public function processRequest() {
-    $request = $this->getRequest();
+  protected function processDiffusionRequest(AphrontRequest $request) {
     $controller = id(new PhabricatorApplicationSearchController())
-      ->setQueryKey($this->queryKey)
+      ->setQueryKey($request->getURIData('queryKey'))
       ->setSearchEngine(new PhabricatorRepositorySearchEngine())
       ->setNavigation($this->buildSideNavView());