Update bestValue when futility pruning (2)

Same idea of 5af8179647
in qsearch() but applied to search()

After 15500 games at 15+0.05
ELO: 4.48 +-3.4 (95%) LOS: 99.5%
Total: 15500 W: 3061 L: 2861 D: 9578

bench: 4985829

src/search.cpp

@@ -879,9 +879,14 @@ split_point_start: // At split points actual search starts from here
 
           if (futilityValue < beta)
           {
-              if (SpNode)
+              bestValue = std::max(bestValue, futilityValue);
-                  splitPoint->mutex.lock();
 
+              if (SpNode)
+              {
+                  splitPoint->mutex.lock();
+                  if (bestValue > splitPoint->bestValue)
+                      splitPoint->bestValue = bestValue;
+              }
               continue;
           }