Show mnemonic doesn't work with encrypted smartcard

Moving discussion to this issue @openoms discovered.

https://github.com/cryptoadvance/specter-diy/pull/157#issuecomment-857570562

> just to check using a smartcard with firmware v1.5.4 the show recovery phrase does not work.
> The device asks for the PIN and returns for the menu without showing the seed.

and https://github.com/cryptoadvance/specter-diy/pull/157#issuecomment-857977250:

> Managed to reproduce the problem, but needs more detail.
> The recovery words are not shown if I switch the device on and proceed to load the keys from the smart card (it is stored encrypted there).
>
> If I switch the device on and generate a keys the words can be shown.
> Then without switching off I can load the keys from the smartcard and in this case the (correct) words are shown again from the menu.
>
> The problem is only when loading the keys from the smartcard without generating keys beforehand.

I was not able to reproduce this issue yet, requires further investigation.