Show mnemonic doesn't work with encrypted smartcard

[stepansnigirev]

Moving discussion to this issue @openoms discovered.

#157 (comment)

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 #157 (comment):

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.