[RC] When paying for a subscription and vaulting fails, cart is cleared (423)

[jorgeatorres]

Describe the bug

When trying to pay for a subscription with DCC using a credit card number that doesn't permit vaulting (for instance, any card from the CC generator), the order is not allowed to continue (which was fixed in #308) but for some reason the whole cart is cleared, which can result in a bunch of strange errors should the user attempt to re-submit the form.

To reproduce

1. Setup DCC with vaulting enabled.
2. Add a subscription product to the cart.
3. Go to https://developer.paypal.com/developer/creditCardGenerator and generate some CC details.
4. Go to Checkout and enter the previously generated card details.
5. Click "Place Order".
6. Confirm that placing order fails because the method wasn't stored in the vault correctly.
7. Click "Place Order" again to see a weird error message.
8. Refresh the page and see the cart has been emptied, preventing users from re-attempting payment.

Screenshots
Screencast:

Expected behavior

Users should be allowed to use other CC details to complete payment. Card shouldn't be cleared.