Fix bug in switch person window where enter button did not work.

ui/login/account_picker/user_pod_row.js

 // 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.
 
 /**
  * @fileoverview User pod row implementation.
  */
 
 cr.define('login', function() {
   /**
@@ skipping 3406 matching lines @@
             else
               this.focusPod(this.firstElementChild);
 
             e.stopPropagation();
           }
           break;
         case 'Enter':
           if (this.focusedPod_) {
             var targetTag = e.target.tagName;
             if (e.target == this.focusedPod_.passwordElement ||
-                e.target == this.focusedPod_.pinKeyboard.inputElement ||
+                (this.focusedPod_.pinKeyboard &&
+                 e.target == this.focusedPod_.pinKeyboard.inputElement) ||
                 (targetTag != 'INPUT' &&
                  targetTag != 'BUTTON' &&
                  targetTag != 'A')) {
               this.setActivatedPod(this.focusedPod_, e);
               e.stopPropagation();
             }
           }
           break;
         case 'Escape':
           if (!this.alwaysFocusSinglePod)
@@ skipping 85 matching lines @@
        if (pod && pod.multiProfilesPolicyApplied) {
          pod.userTypeBubbleElement.classList.remove('bubble-shown');
        }
      }
   };
 
   return {
     PodRow: PodRow
   };
 });