Remove two xors by setting the hash keys for unreachable squares to zero
performance before:
3.6714 +- 0.20% Gcycles
3.6620 +- 0.12% Gcycles
3.6704 +- 0.26% Gcycles
3.6602 +- 0.27% Gcycles
3.6799 +- 0.37% Gcycles
after:
3.6540 +- 0.30% Gcycles
3.6388 +- 0.25% Gcycles
3.6557 +- 0.17% Gcycles
3.6449 +- 0.15% Gcycles
3.6460 +- 0.26% Gcycles
(every line is a different `profile-build` and shows the number of
cycles needed for `./stockfish bench`, measured with `perf stat -r 10`)
closes https://github.com/official-stockfish/Stockfish/pull/5754
No functional change