Improve timeline rendering for old macros

Summary: This always bugs me when I'm going through `secure` looking for the spiciest macros.

Test Plan: Forced a date to be null, saw reasonable text.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D20453

src/applications/macro/controller/PhabricatorMacroViewController.php

@@ -136,7 +136,12 @@ final class PhabricatorMacroViewController
     $image_uri = $handles[$author_phid]->getImageURI();
     $image_href = $handles[$author_phid]->getURI();
 
+    if (!$date) {
+      $content = pht(
+        'Masterfully imagined by %s in ages long past.', $author);
+    } else {
       $content = pht('Masterfully imagined by %s on %s.', $author, $date);
+    }
 
     return id(new PHUIHeadThingView())
       ->setImage($image_uri)