Avoid fatal error if there's no Arcanist project or repository

Test Plan: Display diff without repository

Reviewers: nh, epriestley

Reviewed By: epriestley

CC: aran, Koolvin

Differential Revision: https://secure.phabricator.com/D2373

src/applications/differential/field/specification/revisionstatus/DifferentialRevisionStatusFieldSpecification.php

@@ -35,6 +35,9 @@ final class DifferentialRevisionStatusFieldSpecification
     $info = null;
     $local_vcs = $diff->getSourceControlSystem();
     $backing_vcs = $diff->getBackingVersionControlSystem();
+    if (!$backing_vcs) {
+      $backing_vcs = $local_vcs;
+    }
 
     if ($status == ArcanistDifferentialRevisionStatus::ACCEPTED) {
       if ($local_vcs == $backing_vcs) {

src/applications/differential/storage/diff/DifferentialDiff.php

@@ -91,6 +91,9 @@ final class DifferentialDiff extends DifferentialDAO {
       return null;
     }
     $repository = $arcanist_project->loadRepository();
+    if (!$repository) {
+      return null;
+    }
     return $repository->getVersionControlSystem();
   }