[electrum] fix opening Trezor settings menu while the device is locked

Summary:
For some reason this feature is None when the device is locked, while all other features seem to be properly defined.
Don't raise an error dialog, just disable the passaphrase feature and add a tooltip to explain why it is disabled.

The error was:

    passphrases_label.setText(disen[features.passphrase_protection])
                              ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: list indices must be integers or slices, not NoneType

Test Plan: Open a Trezor wallet, lock the device, open the trezor setting menu (trezor logo in the bottom-right bar)

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D17845