Add hung bots to sheriff-o-matic view

Tools/GardeningServer/model/ct-builder.html

 <!--
 Copyright 2014 The Chromium Authors. All rights reserved.
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
 <script>
 function CTBuilder(masterUrl, builder, firstFailingBuild, failingBuildCount) {
   this.masterUrl = masterUrl;
   this.builder = builder;
   this.firstFailingBuild = firstFailingBuild;
   this.failingBuildCount = failingBuildCount;
-  this.buildUrl = "{1}/builders/{2}/builds/{3}".assign(
-      masterUrl, encodeURIComponent(builder), firstFailingBuild);
+  this.buildUrl = "{1}/builders/{2}".assign(
+      masterUrl, encodeURIComponent(builder));
+  if (firstFailingBuild)
+      this.buildUrl += "/builds/" + firstFailingBuild;
 }
 </script>