Osc 2.3.4.1 php7 products out stock

[ammsimon]

Hello, sorry for the english
php 7 on oscommerce 2.3.4.1
The shop works perfectly, but if the products are out of stock in the cart,
the link to checkout shipping displays an error 500 regardless of the configuration (allow or not orders in negative stock).
The modified files come from the BS version, which does not reproduce the error.
I can not find the error I returned php 5.6
Thank you in advance if anyone has an idea for that.