cmake: do not cache libusb library if libusb-1.0 headers not found
cmake: do not cache libusb library if libusb-1.0 headers not found

Library found might be an older libusb version.

Closes #158


Former-commit-id: 12783e1cfd3902954a9513ca1baf53433add742a
penfold42/hyperion.ng,redPanther/hyperion.ng,hyperion-project/hyperion,hyperion-project/hyperion.ng,penfold42/hyperion.ng,hyperion-project/hyperion,hyperion-project/hyperion,ntim/hyperion,redPanther/hyperion.ng,Funatiq/hyperion.ng,Funatiq/hyperion.ng,hyperion-project/hyperion.ng,ntim/hyperion,Funatiq/hyperion.ng,penfold42/hyperion.ng,redPanther/hyperion.ng,Funatiq/hyperion.ng,hyperion-project/hyperion.ng,penfold42/hyperion.ng,penfold42/hyperion.ng,ntim/hyperion,hyperion-project/hyperion,hyperion-project/hyperion.ng,redPanther/hyperion.ng,hyperion-project/hyperion.ng,hyperion-project/hyperion,hyperion-project/hyperion,redPanther/hyperion.ng,penfold42/hyperion.ng,redPanther/hyperion.ng,ntim/hyperion,ntim/hyperion,Funatiq/hyperion.ng,ntim/hyperion,hyperion-project/hyperion.ng,Funatiq/hyperion.ng