Fix several warnings

htdocs/admin/limits.php

htdocs/cashdesk/class/Facturation.class.php

htdocs/commande/class/commande.class.php

htdocs/compta/facture/class/facture-rec.class.php

htdocs/compta/facture/class/facture.class.php

htdocs/expedition/class/expedition.class.php

htdocs/expensereport/card.php

htdocs/install/upgrade2.php

htdocs/product/card.php

htdocs/supplier_proposal/class/supplier_proposal.class.php