Avoid wrongful TT/history updates when unwinding the search during a …

…thread stop

Probcut does not have the same logic that exists in the primary move loop during pvsearch, which guards against acting on invalid scores from child nodes. With this, it does. The solution, and the comment, are copy-pasted from the other location.

src/search.cpp

@@ -819,6 +819,11 @@ Value Search::Worker::search(
 
             if (value >= probCutBeta)
             {
+                // If a stop occurred, the return value of the search cannot be trusted, and we
+                // must return immediately without updating any histories nor the transposition table.
+                if (threads.stop.load(std::memory_order_relaxed))
+                    return VALUE_ZERO;
+
                 thisThread->captureHistory[movedPiece][move.to_sq()][type_of(captured)]
                   << stat_bonus(depth - 2);