usa una LEFT JOIN

invece di

... FROM `gd_3698_domini`,gd_3565_clienti WHERE id_3565_clienti.id_cliente=gd_3698_domini.`cliente _id` ..

usa

... FROM gd_3565_clienti LEFT JOIN `gd_3698_domini` ON gd_3565_clienti.id_cliente=gd_3698_domini.`cliente _id` ...