Fix an issue where builds with no initiator failed to render in build plans

Summary: See PHI1743. If a build has no initiator PHID, the rendering pathway incorrectly tries to access a handle for it anyway.

Test Plan:
  - Set a build to have no initiator PHID.
  - Viewed the build plan for the build.
  - Before: fatal when trying to access the `null` handle.
  - After: clean build plan rendering.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Differential Revision: https://secure.phabricator.com/D21269

src/applications/harbormaster/view/HarbormasterBuildView.php

@@ -34,7 +34,7 @@ final class HarbormasterBuildView
     $list = new PHUIObjectItemListView();
     foreach ($builds as $build) {
       $id = $build->getID();
-      $initiator = $handles[$build->getInitiatorPHID()];
+
       $buildable_object = $handles[$build->getBuildable()->getBuildablePHID()];
 
       $item = id(new PHUIObjectItemView())
@@ -46,7 +46,9 @@ final class HarbormasterBuildView
         ->setEpoch($build->getDateCreated())
         ->addAttribute($buildable_object->getName());
 
-      if ($initiator) {
+      $initiator_phid = $build->getInitiatorPHID();
+      if ($initiator_phid) {
+        $initiator = $handles[$initiator_phid];
         $item->addByline($initiator->renderLink());
       }