Fixed: find() function returns -1 when not findind a substring.
Fixed: find() function returns -1 when not findind a substring.

makerbot/pyusb,kopchik/pyusb,AlanJAS/pyusb,h3nj3/pyusb,karlp/pyusb,h3nj3/pyusb,makerbot/pyusb,kopchik/pyusb,swinman/pyusb,swinman/pyusb,AlanJAS/pyusb,rabryan/pyusb,rabryan/pyusb,karlp/pyusb