Display donate checkout pane even if donation product is already in the cart

I have multiple donation products on the site and I'm using the uc_donate submodule too. Only one of those donation products is in the relevant nodequeue causing it to appear in the donation checkout pane. However, as soon as the customer adds any donation product (regardless of whether it's in the nodequeue or not) to their cart, the donation pane no longer appears on the checkout pane.

The attached patch removes the check preventing that from happening.