Correct new products query in 2.0.0

[scottcwilson]

SHOW_NEW_PRODUCTS_LIMIT is an int, not a string #6399

Fixes #6398.

Removal of old zen_get_products_new_timelimit to be done as a follow on PR.

[lat9]

My bad; I need to make a list of those Min/Max Values constants that are converted to int values for future use. They bite me every time.

[scottcwilson]

My bad; I need to make a list of those Min/Max Values constants that are converted to int values for future use. They bite me every time.

Hang on ... this means we need documentation in that area!

[scottcwilson]

https://docs.zen-cart.com/dev/code/constants/