make sure there is some quantity before using the / operator

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@6311 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/MovementGroup.py

@@ -785,7 +785,9 @@ class FakeMovement:
     """
       Return average price 
     """
-    return (self.getAddPrice() / self.getAddQuantity())
+    if self.getAddQuantity()>0:
+      return (self.getAddPrice() / self.getAddQuantity())
+    return 0.0
 
   def getAddQuantity(self):
     """