Update the preference controller in search index for battery usage.

BatteryAppListPreferenceController is totally replaced by
BatteryChartPreferenceController now. Update the search index returns.

Bug: 256123455
Test: manual
Change-Id: I2340f1be0cee74771aab293a5df8551325c014be

src/com/android/settings/fuelgauge/batteryusage/BatteryChartPreferenceController.java

@@ -198,7 +198,7 @@ public class BatteryChartPreferenceController extends AbstractPreferenceControll
 
     @Override
     public void onDestroy() {
-        if (mActivity.isChangingConfigurations()) {
+        if (mActivity == null || mActivity.isChangingConfigurations()) {
             BatteryDiffEntry.clearCache();
         }
         mHandler.removeCallbacksAndMessages(/*token=*/ null);