Fix sometimes incorrect prefetches. No functional change.

mstembera · mstembera · commit cddde31eed50 · 2021-10-22T20:01:05.000-07:00
bench: 6154836
diff --git a/src/position.cpp b/src/position.cpp
@@ -1013,9 +1013,9 @@ void Position::do_null_move(StateInfo& newSt) {
   }
 
   st->key ^= Zobrist::side;
-  prefetch(TT.first_entry(key()));
-
   ++st->rule50;
+  prefetch(TT.first_entry(key()));
+  
   st->pliesFromNull = 0;
 
   sideToMove = ~sideToMove;
