Fix settings crash during factory reset.

If you close and then launch settings before the persistent
data block wipe is finished.
Bug: 20458454

Change-Id: I07bf79f25bcb30ac8932925aa7b77b9a95d16e20

src/com/android/settings/MasterClearConfirm.java

@@ -78,9 +78,11 @@ public class MasterClearConfirm extends InstrumentedFragment {
                     @Override
                     protected void onPostExecute(Void aVoid) {
                         mProgressDialog.hide();
+                        if (getActivity() != null) {
                             getActivity().setRequestedOrientation(mOldOrientation);
                             doMasterClear();
                         }
+                    }
 
                     @Override
                     protected void onPreExecute() {