[*] MO : blockcart - ensure the animated product stays within viewport boundaries

When a product is added in the cart, an animated "shadow" product goes from the product's image to the cart block.

This shadow product can sometimes go too far on the right (for example, when it is very large). This can make an horizontal scrollbar appear, or even make the whole page zoom out (for instance, on a tablet or smart phone).

This is a quick fix to ensure the shadow product can never get farther on the right than the cart block.

Regards,