title: Prestashop: Display products from childcategories if parent category is empty
body: <p>Please help me with the following:</p>
  
  <p>My website shows, when chossing a category, the corresponding sub-categories, and the message "there are no products in this category". This happens while drilling-down until one arrives to the lower level sub-category.</p>
  
  <p>I would like to show all the products of its sub-categories instead.</p>
  
  <p>How can I do this please?</p>
  
  <p>Thanks a lot for your advice,</p>
  
  <p>Steven </p>