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

@@ -78,8 +78,10 @@ public class MasterClearConfirm extends InstrumentedFragment {
                     @Override
                     protected void onPostExecute(Void aVoid) {
                         mProgressDialog.hide();
-                        getActivity().setRequestedOrientation(mOldOrientation);
-                        doMasterClear();
+                        if (getActivity() != null) {
+                            getActivity().setRequestedOrientation(mOldOrientation);
+                            doMasterClear();
+                        }
                     }
 
                     @Override