hardware usb connection isn't properly closed

[wouterverweirder]

I noticed an issue with the hardware shutdown code. The claimed usb device isn't properly released, which causes issues when you create a new instance of the hardware layer without shutting down. Fix would be:

• initialize the dev pointer to zero in the constructor.

• adjust the shutdown code to contain the following:

  if(dev != 0) { libusb_close(dev); libusb_release_interface(dev, 0); } libusb_exit(ctx);

this closes & releases the dev handle properly