Fix a possible memory use after free and leak situation associated
with USB device detach when using character device handles. This also
includes LibUSB. It turns out that "usb_close()" cannot always get a
reference to clean up its USB transfers and such, if called during the
kernel USB device detach.

Analysis by: hselasky @
Reported by: Juergen Lock <nox@jelal.kn-bremen.de>
MFC after: 1 week