Fix crash when activity not attached after search index finishes.

When search indexing completes, check for valid  activity before
proceeding with further operations.

Change-Id: I7c72aa358574f79e2184d60bc9d0241595ea5d3b
Fix: 38198223
Test: make RunSettingsRoboTests

src/com/android/settings/search2/SearchFragment.java

@@ -291,6 +291,9 @@ public class SearchFragment extends InstrumentedFragment implements SearchView.O
      */
     @Override
     public void onIndexingFinished() {
+        if (getActivity() == null) {
+            return;
+        }
         if (mShowingSavedQuery) {
             mSavedQueryController.loadSavedQueries();
         } else {