When creating a new wallet in a Electrum instance with existing wallets
this change forces the user to reuse a password of any existing wallet
if `SimpleConfig.WALLET_USE_SINGLE_PASSWORD` is True.
This prevents the amount of different passwords from increasing and
guides the user towards a single wallet password (the intended default).
- fix: qml gui errors when trying to open a wallets with only keystore-encryption
- fixes https://github.com/spesmilo/electrum/issues/10171
- qml gui to prompt for password on wallet open even if wallet is not storage-encrypted
