Avoid a division by zero

mrp_average_cost/mrp.py

@@ -305,6 +305,9 @@ class MrpProduction(orm.Model):
         # so we consider that standard_price is in company currency
         # It will not work if you are in multi-company environment
         # with companies in different currencies
+        if not qty_before_mo + mo_qty_product_uom:
+            new_std_price = mo_standard_price
+        else:
             new_std_price = (
                 (product.standard_price * qty_before_mo) +
                 (mo_standard_price * mo_qty_product_uom)) / \