Fix a fatal when viewing a daemon task with an invalid ID

Summary:
Fixes T11295. Prior to this change, the "404 page" for daemon tasks fatals.

This page is special cased a little bit and not a normal 404 page, because it's possible for you to click a valid link and the task to get GC'd by the time you load the page, or similar. It tries to be a little more user-friendly than a bare 404.

Test Plan:
  - Visited `/daemon/task/1428348920328/` (any invalid ID).
  - Now got a nice "no such task" page.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11295

Differential Revision: https://secure.phabricator.com/D16254

src/applications/daemon/controller/PhabricatorWorkerTaskDetailController.php

@@ -15,9 +15,13 @@ final class PhabricatorWorkerTaskDetailController
       $task = reset($tasks);
     }
 
+    $header = new PHUIHeaderView();
+
     if (!$task) {
       $title = pht('Task Does Not Exist');
 
+      $header->setHeader(pht('Task %d Missing', $id));
+
       $error_view = new PHUIInfoView();
       $error_view->setTitle(pht('No Such Task'));
       $error_view->appendChild(phutil_tag(
@@ -30,11 +34,11 @@ final class PhabricatorWorkerTaskDetailController
     } else {
       $title = pht('Task %d', $task->getID());
 
-      $header = id(new PHUIHeaderView())
-        ->setHeader(pht('Task %d: %s',
+      $header->setHeader(
+        pht(
+          'Task %d: %s',
           $task->getID(),
-          $task->getTaskClass()))
-        ->setHeaderIcon('fa-sort');
+          $task->getTaskClass()));
 
       $properties = $this->buildPropertyListView($task);
 
@@ -59,6 +63,8 @@ final class PhabricatorWorkerTaskDetailController
       );
     }
 
+    $header->setHeaderIcon('fa-sort');
+
     $crumbs = $this->buildApplicationCrumbs();
     $crumbs->addTextCrumb($title);
     $crumbs->setBorder(true);