HOTFIX 2016.1, 2016.2, 2016.3, 2016.4 - Americart - Opcode fix

AmeriCart: fixed an issue where no items would get added to the cart if at least one item in the request had a required opcode – whether or not the item actually had a quantity that was being added. Now, the required opcode will not be processed if the quantity of the item is 0.