Sylius version affected: 2.0.2

Description
When you navigate to the cart promotion index, an error division by zero can occur if a promotion has the field Usage limit set to zero.

Steps to reproduce

1. Go to the administration panel.
2. In the Marketing section click on "Cart promotion".
3. Edit a promotion or create a new one.
4. Set the Usage limit to 0 and save.
5. Return to the "Cart promotion" list.

This procedure works on Sylius demonstration instance.

Possible Solution

Replace {% if data.usageLimit is empty %} with {% if not data.usageLimit %} in src/Sylius/Bundle/AdminBundle/templates/promotion/grid/field/usage.html.twig line 1.