[FO] Enhancement - pagination - nbr products/page

I make this edit in most of my project.
It allows to keep a number of 'products per page' related to original value.
It's important in advanced layout (products display by col and not by row like in default template)

(I prefer check if PS_PRODUCT_PER_PAGE is != 0, but with !=10 it keeps original setting (10,20,50))