title: Set default combination automaticly based on stock Prestashop 1.7
body: <p>i need Prestashop to:
  Check stock of combinations from a product.
  If a combination is out of stock, set default combination to a different combination which is in stock.</p>
  
  <p>This way the shop will not show : 'out of stock' at the product, on the category listing. Makes no sense, because the product is not out of stock, only 1 combination is out of stock.</p>
  
  <p>Another solution will be: the out of stock sticker to check if there are any combinations in stock.
  Please do not advise any modules.</p>
  
  <hr>
  
  <p>Example given: </p>
  
  <p>T-shirt in size Small, Medium and Large.
  Small: 0 stock, Medium: 10 stock, Large: 10 stock.
  Prestashop will now show T-shirt as out of stock on the frontend, unless i manually check Medium or Large as a default size.</p>