Keep mate PVs intact.
do not return a cutoff value in razoring if that value is in the mate/tb range.
passed STC:
https://tests.stockfishchess.org/tests/view/666381880ff7cb4868d1fe58
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 130848 W: 34046 L: 33931 D: 62871
Ptnml(0-2): 429, 14968, 34524, 15065, 438
passed LTC:
https://tests.stockfishchess.org/tests/view/66643f120612cd151f9e7788
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 39702 W: 10157 L: 9959 D: 19586
Ptnml(0-2): 20, 4108, 11402, 4296, 25
closes https://github.com/official-stockfish/Stockfish/pull/5379
Bench: 1174094