fix patch from master -> stable migration

cosmogramme/sql/patch/patch_239.php

 <?php
 $adapter = Zend_Registry::get('sql');
-$adapter->query('CREATE TABLE `harvest_log` ( '
+$adapter->query('CREATE TABLE if not exists `harvest_log` ( '
 								. 'id int(11) unsigned not null auto_increment,'
 								. '`type_doc` int(11) not null,'
 								. '`end_date` varchar(10) not null,'