bytetest: fix debug messages not printing negative offset correctly
Unit-tests exposing a bug in byte_test, byte_jump and byte_extract.

Bug emanates from all the keywords being unable to handle negative offsets
when the inspection pointer is at the end of the buffer.
Fix the bug specified in the previous commit.

Bug emanates from byte_test, byte_jump and byte_extract keyword being
unable to handle negative offsets when the inspection pointer is at the
end of the buffer.