Save preferences before updating QBtSession.

src/addnewtorrentdialog.cpp

@@ -596,6 +596,7 @@ void AddNewTorrentDialog::on_buttonBox_accepted()
   pref.useAdditionDialog(!ui->never_show_cb->isChecked());
   if (ui->default_save_path_cb->isChecked()) {
     pref.setSavePath(ui->save_path_combo->itemData(ui->save_path_combo->currentIndex()).toString());
+    pref.sync();
     QBtSession::instance()->configureSession();
   }
 }