sint-list->bytevector raises an error if given list contains 0

[Takashi Kato]

This shouldn't be an error

(sint-list->bytevector '(0) (endianness littel) 1)

But raises an error.

[Takashi Kato]

Modified bytevector-sint-set! to pass 0 without 2 compliant (Fixes #97)

→ <<cset ad2a613d6f1d>>