On new order should check if order is already closed.

[jorix]

"shop_and_order.php" allows add products when no exist a open date for order.

As to reproduce:

• Begin an order.
• Close the order in another browser.
• Add a product, oops! tells us that it has been successfully saved!!
  • but luckily!, the product is not added.
  • a new open order exist but we can't even see or close.
• If we modify existing quantities also tells us that it has been successfully saved!!
  • but luckily!, not is true!

This patch aims to prevent add products when closed date. And also notify to the user that their data has not been saved.