Bug fixed in cn-cbor library

[batyrkhan14]

When encoding cn_cbor structure before writing any chunk of bytes into
buffer, library ensures that there is enough space to write current
chunk. It is done by the following inequality: offset+length >= size.
If inequality is true, then library decides that there is no enough space.
However, if offset+length == size then there is still enough space to
write a chunk of size length.

[sbertin-telular]

This same change is also in #25 and the same problem also fixed by #49.