Tweak history initialization
Simplify initialization of continuation history by using everywhere the same starting value.
STC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 90952 W: 24312 L: 24153 D: 42487
Ptnml(0-2): 356, 10168, 24290, 10285, 377
https://tests.stockfishchess.org/tests/view/
633948f235f43d649ff61fd0
LTC:
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 162416 W: 43540 L: 43466 D: 75410
Ptnml(0-2): 77, 16289, 48417, 16333, 92
https://tests.stockfishchess.org/tests/view/
6339ee8a35f43d649ff63986
closes https://github.com/official-stockfish/Stockfish/pull/4186
Bench:
4156027