[-] MO : gsitemap, removed an important infinite loop and bugfixs

In the _getProductLink function, the sql WHERE clause "`id_product` >= '.intval($id_product).'" is very important.
During generation, if the shop has more than ~5000 products, the memory limit in _addLinkToSitemap make a redirect for a new sitemap file creation and put the next product id as link parameter for a correct generation start.
The parameter was not used, so an infinite loop start with infinite generated files on the server.