Fix Illegal PV (#115)

Elo   | 0.98 +- 2.90 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=8MB
LLR   | 2.96 (-2.94, 2.94) [-5.00, 0.00]
Games | N: 16686 W: 4079 L: 4032 D: 8575
Penta | [169, 1830, 4300, 1873, 171]
https://chess.aronpetkovski.com/test/2832/

bench 1849271

Author: xu-shawn

Serendipity/src/main/java/org/shawn/games/Serendipity/Search/AlphaBeta.java

@@ -74,8 +74,7 @@ public AlphaBeta(TranspositionTable tt, NNUE network)
 	private void updatePV(Move move, int ply)
 	{
 		threadData.pv[ply][0] = move;
-		System.arraycopy(threadData.pv[ply + 1], 0, threadData.pv[ply], 1, MAX_PLY - 1);
-		threadData.pv[ply + 1][0] = null;
+		System.arraycopy(threadData.pv[ply + 1], 0, threadData.pv[ply], 1, MAX_PLY);
 	}
 
 	private void clearPV()
@@ -284,6 +283,11 @@ private int mainSearch(Board board, int depth, int alpha, int beta, int ply, boo
 		inCheck = sse.inCheck = board.isKingAttacked();
 		inSingularSearch = sse.excludedMove != null;
 
+		if (isPV)
+		{
+			threadData.pv[ply][0] = null;
+		}
+
 		if ((nodesCount & 1023) == 0 && (timeManager.shouldStop() || (nodesLimit > 0 && nodesCount > nodesLimit)))
 		{
 			throw new TimeOutException();
@@ -577,9 +581,9 @@ else if (givesCheck)
 				r -= isPV ? 1 : 0;
 				r -= givesCheck ? 1 : 0;
 				r += cutNode ? 1 : 0;
-				
+
 				final int history = threadData.history.get(board, move) + 4500;
-				
+
 				r -= history / 5000;
 
 				int d = newdepth - r;