Segfault on disconnecting USB adapter when pairing about xow

[medusalix]

Thanks for the detailed bug report and the stack trace 😃. It could be some kind of bug in libusb's implementation of libusb_control_transfer. Could you dig a little bit deeper to find the place/line where libusb_control_transfer is failing (maybe using gdb)?

[StopMotionCuber]

Well, the problem is that handle is a nullpointer and libusb_control_transfer does not like nullpointer as handles.
I'm not sure how to handle that correctly (pun intended).

Also there is a use after free in Log::error("Error in bulk read: %d", transfer->status); as transfer is freed already. I was too lazy to make a PR for that, please fix in one of your commits.

[medusalix]

Ah, now I see. So UsbDevice::close sets the handle to nullptr while the dongle thread is still doing its control transfers. The only reason this is being done is to prevent UsbDevice::open from opening the device multiple times. I'm going to replace this with a boolean variable to indicate if the device is currently open. libusb_control_transfer will probably return LIBUSB_ERROR_NO_DEVICE but thats at least better than a crash.

Also there is a use after free

Good catch 👍. Will push that together with the other fix.

[medusalix]

@StopMotionCuber I've put checks into place that handle the edge case of removing the device while the pairing is in progress. This also has the benefit of logging the exact place where it errors (as one would expect). Please see if commit 365c2bc fixes your issues.