Situation 1: device was disconnected and not reconnected
User expectation: selecting the device in the device dropdown shouldn't be possible anymore
Current behavior: selecting the device is possible but the session is empty (no device)
Possible solution: when libusb tells libsigrok that the USB device was disconnected, it should tell PV so that the entry can be greyed out
Also, when the device is reconnected, the entry should become enabled again.
This however seems tricky to implement in libsigrok as it's unclear how libsigrok would be able to determine that the newly connected USB device is a device that was connected before. Maybe a device scan should be initiated by libsigrok every time a USB device is connected?