Fix uber tray crash on stumpy which has no battery

ash/system/settings/tray_settings.cc

Index: ash/system/settings/tray_settings.cc
diff --git a/ash/system/settings/tray_settings.cc b/ash/system/settings/tray_settings.cc
index 49ba7300694f58cece954c67fe5ab218e4bb3fc0..3be23862f53a37bfa9904faa26ee4ca1d1dde5c3 100644
--- a/ash/system/settings/tray_settings.cc
+++ b/ash/system/settings/tray_settings.cc
@@ -69,8 +69,9 @@ class SettingsDefaultView : public ash::internal::ActionableView {
   virtual ~SettingsDefaultView() {}
 
   void UpdatePowerStatus(const PowerSupplyStatus& status) {
-    if (power_status_view_)
-      power_status_view_->UpdatePowerStatus(status);
+    if (!power_status_view_)
+      return;
+    power_status_view_->UpdatePowerStatus(status);
     string16 accessible_name = label_ ?
         label_->text() + ASCIIToUTF16(", ") +
             power_status_view_->accessible_name() :