Prevent buildable list in Harbormaster from breaking when container or buildables are missing

Summary: Ref T1049.  I'm fair sure this is just a case of bad data in my local install, but we probably don't want the default page for Harbormaster to break when there's invalid / missing container or buildable handles on any of the builds.

Test Plan: Loaded the page, didn't get a crash due to null reference.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: demo, epriestley, Korvin

Maniphest Tasks: T1049

Differential Revision: https://secure.phabricator.com/D8608

src/applications/harbormaster/controller/HarbormasterBuildableListController.php

@@ -37,8 +37,12 @@ final class HarbormasterBuildableListController
 
       $item = id(new PHUIObjectItemView())
         ->setHeader(pht('Buildable %d', $buildable->getID()));
-      $item->addAttribute($buildable->getContainerHandle()->getName());
-      $item->addAttribute($buildable->getBuildableHandle()->getFullName());
+      if ($buildable->getContainerHandle() !== null) {
+        $item->addAttribute($buildable->getContainerHandle()->getName());
+      }
+      if ($buildable->getBuildableHandle() !== null) {
+        $item->addAttribute($buildable->getBuildableHandle()->getFullName());
+      }
 
       if ($id) {
         $item->setHref("/B{$id}");