HidChannel panics when USB device is unplugged

[iinuwa]

If you unplug the device while trying to send something to it, the library panics. We'll need to clean turn this map this error instead:

https://github.com/linux-credentials/libwebauthn/blob/master/libwebauthn/src/transport/hid/channel.rs#L267

I found this while testing linux-credentials/credentialsd#16.

[AlfioEmanueleFresta]

Thanks @iinuwa, fixed in #109.