Not possible to assign service point as default carrier

Hello,

I've found a bug on your module running on PS 1.7.8. 

Service point carriers cannot be selected as default carriers in the Prestashop back office. As a result, when adding a product to the cart, the customer sees the price of the next standard carrier, which in my case is more expensive. I therefore have a high rate of shopping cart abandonment as a result. 

Sincerely,

Nathan. 