Double 'id_image' definition in product getList

Double 'id_image' definition in product getList, the correct on is : MAX('.$alias_image.'.id_image) id_image, I remove the second.

The problem was, sometimes, image product was not display in multi-shop in the BO.
Merge pull request #403 from MrManchot/patch-4

Double 'id_image' definition in product getList