ERP5Workflow: use cell method

instead of re-coding the wheel

product/ERP5Workflow/Document/PermissionRoles.py

@@ -111,8 +111,10 @@ class PermissionRoles(XMLObject):
 
     state = self.getParentValue()
     cell_range = state.getCellRange()
-    cell_permission = sorted(cell_range[0])[self._getPermissionIndex()]
-    cell_role = sorted(cell_range[1])[self._getRoleIndex()]
+
+    cell_permission = self._getPermission()
+    cell_role = self._getRole()
+
     # update the state permission structure to take into account
     # the selection/non-selection of this cell
     if value and (cell_role not in state.state_permission_roles[cell_permission]):