Better exception message

[yanguoyu]

1. I open the wallet and open Nervos app and connect the wallet
2. The wallet auto-locked after a few minutes
3. Now I call signTransaction and it throws an unknown exception(Ledger device: UNKNOWN_ERROR (0x6804) Error: Ledger device: UNKNOWN_ERROR (0x6804))

Can it throw a standard exception or support to get wallet locked status?