[OPTIM] halog: use a faster zero test in fgets()

[OPTIM] halog: use a faster zero test in fgets()

A new idea came up to detect the presence of a null byte in a word.
It saves several operations compared to the previous one, and eliminates
the jumps (about 6 instructions which can run 2-by-2 in parallel).

This sole optimisation improved the line count speed by about 30%.