Invalid keys when switching smartcard from ed25519 to other curves

[NIIBE Yutaka]

Trevor Bentley wrote:
> Just want to follow up on this again and see if anybody has any 
> opinions.  I have included a small patch to fix it:

I see the problem.  I think that it is the call of ask_curve from
ask_card_keyattr in card-util.c.  Isn't it?

(Looking your patch with the context of keygen.c, I didn't understand
why ask_curve matters.)

I'll apply your patch.
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