Please provide 'cardInvalid(...)' method in CardValidCallback interface

[Mr-Goldberg]

In my code I need to enable/disable 'save card' button dynamically. Case: I can disable 'save card' button by default, and then enable it when card became valid (from callback). But if user will edit the card info then - it may became invalid, and there is no way to know about it, while user types. I think I can do it in 'hacky' way, but no reason for this :) Please provide such callback.