sanei_usb: allow non-configured devices on macOS for libusb-1.x

This is an attempt to address the comments requested several months ago in !219 (closed) and discussed in #38. In principle this is an identical patch to !219 (closed) with the exception of also disabling misleading log messages when running on macOS. In addition there was a compile error in an unrelated portion of the code on macOS that I fixed in order to be able to build on my machine running macOS 10.15.3.