cowboy commit -- fixing fatal I introduced from D4174

Summary: we don't always have a diff so instead set an explicit title in the controller.

Test Plan: no more fatals. grepped carefully for every call site and tested them all

src/applications/differential/controller/DifferentialDiffViewController.php

@@ -132,6 +132,8 @@ final class DifferentialDiffViewController extends DifferentialController {
       ->setVisibleChangesets($changesets)
       ->setRenderingReferences($refs)
       ->setStandaloneURI('/differential/changeset/')
+      ->setDiff($diff)
+      ->setTitle('D'.$diff->getID());
       ->setUser($request->getUser());
 
     return $this->buildStandardPageResponse(

src/applications/differential/controller/DifferentialRevisionViewController.php

@@ -304,6 +304,7 @@ final class DifferentialRevisionViewController extends DifferentialController {
       $changeset_view->setRepository($repository);
     }
     $changeset_view->setSymbolIndexes($symbol_indexes);
+    $changeset_view->setTitle('D'.$target->getID());
 
     $diff_history = new DifferentialRevisionUpdateHistoryView();
     $diff_history->setDiffs($diffs);

src/applications/differential/view/DifferentialChangesetListView.php

@@ -20,6 +20,16 @@ final class DifferentialChangesetListView extends AphrontView {
   private $diff;
   private $vsMap = array();
 
+  private $title;
+  
+  public function setTitle($title) {
+    $this->title = $title;
+    return $this;
+  }
+  private function getTitle() {
+    return $this->title;
+  }
+
   public function setBranch($branch) {
     $this->branch = $branch;
     return $this;
@@ -190,7 +200,7 @@ final class DifferentialChangesetListView extends AphrontView {
 
     return
       id(new PhabricatorHeaderView())
-        ->setHeader('D'.$this->diff->getID())
+        ->setHeader($this->getTitle())
         ->render().
       phutil_render_tag(
       'div',

src/applications/diffusion/controller/DiffusionChangeController.php

@@ -15,12 +15,15 @@ final class DiffusionChangeController extends DiffusionController {
       return new Aphront404Response();
     }
     
-    $callsign = $drequest->getRepository()->getCallsign();
+    $repository = $drequest->getRepository();
+    $callsign = $repository->getCallsign();
+    $commit = $drequest->getRawCommit();
     $changesets = array(
       0 => $changeset,
     );
 
     $changeset_view = new DifferentialChangesetListView();
+    $changeset_view->setTitle(DiffusionView::nameCommit($repository, $commit));
     $changeset_view->setChangesets($changesets);
     $changeset_view->setVisibleChangesets($changesets);
     $changeset_view->setRenderingReferences(

src/applications/diffusion/controller/DiffusionCommitController.php

@@ -257,7 +257,12 @@ final class DiffusionCommitController extends DiffusionController {
         }
       }
 
+      $change_list_title = DiffusionView::nameCommit(
+        $repository,
+        $commit->getCommitIdentifier()
+      );
       $change_list = new DifferentialChangesetListView();
+      $change_list->setTitle($change_list_title);
       $change_list->setChangesets($changesets);
       $change_list->setVisibleChangesets($visible_changesets);
       $change_list->setRenderingReferences($references);