WorkflowTool.py: resolve getTypeInfo error when add gadget in access tab.

product/ERP5/Tool/WorkflowTool.py

@@ -700,6 +700,8 @@ class WorkflowTool(BaseTool, OriginalWorkflowTool):
     worklist_dict = {}
 
     document = info.object
+    document_pt = None
+    if document is not None:
       document_pt = document.getTypeInfo()
 
     if document_pt is not None: