do not assume there is always a solve and diverge method

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@3897 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/Delivery.py

@@ -279,6 +279,7 @@ class Delivery(XMLObject):
       deliver is convergent, and if so it will put the delivery
       in a solved state, if not convergent in a diverged state
       """
+      if hasattr(self,'diverge') and hasattr(self,'converge'):
         if self.isDivergent():
           self.diverge()
         else: