Correctly initialize libusb 1.0

gphoto2 --auto-detect segfaults with libusb 1.0 being used.
The cause for this has been analyzed by Peter Stuge (maintainer libusb) and he took the time to write a patch for libgphoto2.

Patch attached

Issue; if libusb_init is not started with default context (null), then the context used needs to be passed ro subsequent calls of other libusb_ calls as well. This was not happening in every case.