⚖ Pawn scaling: don't allow scores to change sign

[eduherminio]

Includes similar fix as #828, and also prevents a winning score to transform into a losing one, and viceversa

Test  | bugfix/eg-pawn-scaling-no-sign-change
Elo   | -0.68 +- 2.80 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=32MB
LLR   | -2.26 (-2.25, 2.89) [0.00, 3.00]
Games | 36748: +11429 -11501 =13818
Penta | [1299, 3990, 7771, 4112, 1202]
https://openbench.lynx-chess.com/test/424/

but

> python .\sprt.py -w 11429 -d 13818 -l 11501 -e0 -5 -e1 0
ELO: -0.681 +- 2.8 [-3.48, 2.12]
LLR: 3.07 [-5.0, 0.0] (-2.94, 2.94)
H1 Accepted