Fix an overflow in SEE

If the stage is King and incremented by one, the stage would overflow leading to reading from bitboards that, in this context, are nonsensical

Passed Non-Regr:
Elo   | 29.49 +- 12.84 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=8MB
LLR   | 2.91 (-2.25, 2.89) [-5.00, 0.00]
Games | N: 1358 W: 384 L: 269 D: 705
Penta | [8, 136, 293, 217, 25]
https://aytchell.eu.pythonanywhere.com/test/710/

bench 7874387

src/searchUtil.h

@@ -105,7 +105,7 @@ inline bool see(Position &pos, int threshold, Move move) {
             continue;
         }
 
-        while (!attackers[stm] && stages[stm] < KING + 1) {
+        while (!attackers[stm] && stages[stm] < KING) {
             stage = PieceType(++stages[stm]);
             attackers[stm] |= getAttacks(stages[stm], to, blockers, !stm) & pos.getPieces(stm, stage) & blockers;
         }