Concurrent checkouts can lead to negative stock

Hello, I'm looking for someone to solve the below issue in OpenCart: Description When two customers check out concurrently for the same product and the total quantity being ordered is greater than the quantity available, the stock can become negative even if the ‘Store Checkout’ setting under Stock is set to ‘no’. Steps to reproduce Start site, create two customers, create/pick test product and allocate some stock. Both customers add the product to their carts such that each cart individually is under the available stock, but combined they exceed the available stock. Perform a checkout concurrently, making sure both customers finish checkout (click the ‘Confirm Order’ button) as close to the same time as possible. We have reproduced this behavior on a single machine, by performing the above steps by simulating one customer in one browser window and another customer in a second browser window. Expected Result One of the two checkouts fails to complete. Actual Result Both checkouts succeed and the quantity for the product is negative in the admin console.