Submit card-selection form if there is only one card option

With #1 and #2 merged, this extension is almost perfect -- but it stops short at choosing my card, and then leaves me to click submit on the funding selection page.

I don't know if there's actually a scenario where you can end up submitting the order from this page, but I doubt it.

My code only continues if there's only one card option; multiple card options are left to the user to resolve.