Existing ShoppingCartItem Quantity Doubled After Calling "CreateOrder"

[pkmccaffrey]

When calling OrdersController.CreateOrder(), the quantity for any already existing ShoppingCartItem object is doubled.

The issue is in OrdersController.AddOrderItemsToCart(). When calling _shoppingCartService.AddToCart(), Nop assumes that you want to increase the quantity of any pre-existing cart items by the specified amount. This code is called strictly from CreateOrder, so it can be assumed that the quantity submitted for a given OrderItemDto is the desired quantity (and any existing quantity on a ShoppingCartItem should be ignored).

[pkmccaffrey]

A fix for this is included in PR #174 . Due to my own poor planning, this commit does not exist on its own, but in a branch with other enhancements.