more changes

pkg/cart/mutation_change_quantity.go

@@ -32,6 +32,9 @@ func (c *CartMutationContext) ChangeQuantity(g *CartGrain, m *messages.ChangeQua
 	if m == nil {
 		return fmt.Errorf("ChangeQuantity: nil payload")
 	}
+	if g.PaymentInProgress > 0 {
+		return ErrPaymentInProgress
+	}
 	ctx := context.Background()
 
 	foundIndex := -1