Core: fix bug in libusb_has_capability()

The problem was detected by clang on Mac OS X:
warning: use of logical '&&' with constant operand [-Wconstant-logical-operand]
note: use '&' for a bitwise operation

We want to use a bitwise operation and not a logical operation.
OS X: Don't try to work around buggy devices with bInterval = 0 on isochronous...
libusbx 1.0.15-rc3