Fix: avoid warning with php 5.4 and strict mode

htdocs/comm/action/class/actioncomm.class.php

htdocs/contact/canvas/default/tpl/contactcard_edit.tpl.php

htdocs/contact/fiche.php

htdocs/core/ajax/ajaxdirpreview.php

htdocs/core/ajax/ajaxdirtree.php

htdocs/core/boxes/box_activity.php

htdocs/core/class/html.form.class.php

htdocs/core/lib/functions.lib.php

htdocs/core/lib/product.lib.php

htdocs/core/lib/security.lib.php

htdocs/fourn/class/fournisseur.facture.class.php

htdocs/main.inc.php

htdocs/product/class/product.class.php

htdocs/product/class/service.class.php

htdocs/product/fiche.php

htdocs/product/index.php

htdocs/projet/class/task.class.php

htdocs/societe/class/address.class.php

htdocs/user/class/user.class.php

htdocs/user/class/usergroup.class.php