MovementGroup.getAveragePrice: fix possible ZeroDivisionError

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@41892 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/MovementGroup.py

@@ -404,8 +404,10 @@ class FakeMovement:
     price_dict = self._getPriceDict()
     if len(price_dict) == 1:
       return price_dict.keys()[0]
-    return sum(price * quantity for price, quantity in price_dict.items()) / \
-           float(sum(price_dict.values()))
+    total_quantity = sum(price_dict.values())
+    return (total_quantity and
+      sum(price * quantity for price, quantity in price_dict.items())
+      / float(total_quantity))
 
   def getAddQuantity(self):
     """