test_endian: fix signedness warning
test_endian: fix signedness warning

mgjv/libusual,mgjv/libusual,mgjv/libusual,mgjv/libusual,ifduyue/libusual,rabbitt/libusual,markokr/libusual,rabbitt/libusual,ifduyue/libusual,markokr/libusual,markokr/libusual,ifduyue/libusual,rabbitt/libusual,rabbitt/libusual,ifduyue/libusual,markokr/libusual