Fix a noise problem / smaller and faster for the best experience

[saitoha]

Suppress noise

bc76273 has a bug that causes noise.

This problem is fixed by 82dbc28

Compression improvement

The output SIXEL data converted from the test image is reduced again in size by 4.7%.

$ ./gosr snake.jpg|wc -c
394741

Performance improvement

New patch is faster than previous one by 5.2%.

$ seq 1 10|while read i ;do time ./gosr snake.jpg > /dev/null; done 2>&1|awk '{sum+=$11;c++}END{print(sum/c)}'
0.847

[mattn]

Thank you