Fix for Adding the product twice crash

Apparently, this area of availability was never covered with tests. Recent changes in 14101a1 introduced a simple bug with column name. This commit fixes this and adds one test to show this.

rails_application/app/controllers/client/orders_controller.rb

@@ -32,7 +32,7 @@ def edit
 
     def add_item
       read_model = ClientOrders::OrderLine.where(order_uid: params[:id], product_id: params[:product_id]).first
-      unless Availability.approximately_available?(params[:product_id], (read_model&.quantity || 0) + 1)
+      unless Availability.approximately_available?(params[:product_id], (read_model&.product_quantity || 0) + 1)
         redirect_to edit_client_order_path(params[:id]),
                     alert: "Product not available in requested quantity!" and return
       end

rails_application/test/integration/client_orders_test.rb

@@ -98,6 +98,19 @@ def test_paid_orders_summary
     assert_orders_summary("$11.00")
   end
 
+  def test_adding_the_same_product_twice_bug
+    customer_id = register_customer("Customer Shop")
+    product_id = register_product("Fearless Refactoring", 4, 10)
+    Sidekiq::Job.drain_all
+
+    login(customer_id)
+    visit_client_orders
+
+    order_id = SecureRandom.uuid
+    as_client_add_item_to_basket_for_order(product_id, order_id)
+    as_client_add_item_to_basket_for_order(product_id, order_id)
+  end
+
   private
 
   def submit_order_for_customer(customer_id, order_id)