Update UserBulkProcessingForm.class.php

allowing access for eventlisteners (e.g. https://github.com/JoshsBoard/de.joshsboard.jcoins/blob/2af2373132e9a37fd1fece7b59e86262fb9ec801/files/lib/system/event/listener/JCoinsAddMassProcessingListener.class.php#L47 )