fix an error raised by nodejs 0.10 : [TypeError: offset is not uint] on Buffer.writeUInt8 called without offset.
fix an error raised by nodejs 0.10 : [TypeError: offset is not uint] on Buffer.writeUInt8 called without offset.

Signed-off-by: Wilfried Chauveau <0603613de1e704d4e732d4e737829bd81249e803@gmail.com>

ithinuel/mqttsn-packet