erp5_workflow: in convertWorkflow, only reassign the portal type which exist in _chains_by_type.

bt5/erp5_workflow/SkinTemplateItem/portal_skins/erp5_workflow/WorkflowTool_convertWorkflow.xml

@@ -87,8 +87,7 @@ for dc_wf in selected_wf_list:\n
   workflow = context.dc_workflow_asERP5Object(context, dc_wf, temp=0)\n
   selected_wf_id_list.append(dc_wf.id)\n
 \n
-\n
-  for ptype_id in context.getChainDict():\n
+  for ptype_id in context.getChainsByType():\n
     ptype = getattr(context.getPortalObject().portal_types, ptype_id)\n
     # 1. clean DC workflow assignement:\n
     context.delTypeCBT(ptype.id, dc_wf.id)\n