if no list_action are defined on listbox, don't display link. Make this available for all list style (see http://svn.erp5.org/?view=revision&revision=26172 )

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@34192 20353a03-c40f-0410-a6d1-a30d3c3de9de