WorkflowTool.py: resolve the error when state has no premission_roles, matrix...

WorkflowTool.py: resolve the error when state has no premission_roles, matrix index should not be generated.

product/ERP5/Tool/WorkflowTool.py

@@ -352,6 +352,7 @@ class WorkflowTool(BaseTool, OriginalWorkflowTool):
           state.setDescription(sdef.description)
           permission_roles = sdef.permission_roles
           state.setStatePermissionRoles(permission_roles)
+          if sdef.permission_roles is not None:
             state.setCellRange(sorted(sdef.permission_roles.keys()),
                   sorted(workflow.getRoleList()),
                   base_id='cell')