An attempt at official-stockfish#2717. Check if handling search again…

… counter locally per thread helps. Use same TC and threads (but with low throughput) as test 6272a6afc8f14123163c1997 where this was known to occur. I may try to check pgns from time to time and stop the test earlier if the issue persists. Bench: 5845802

src/search.cpp

@@ -314,6 +314,7 @@ void Thread::search() {
   optimism[~us] = -optimism[us];
 
   int searchAgainCounter = 0;
+  bool increaseThreadDepth = true;
 
   // Iterative deepening loop until requested to stop or the target depth is reached
   while (   ++rootDepth < MAX_PLY
@@ -333,7 +334,13 @@ void Thread::search() {
       pvLast = 0;
 
       if (!Threads.increaseDepth)
-         searchAgainCounter++;
+          increaseThreadDepth = false;
+
+      if (!increaseThreadDepth)
+      {
+          searchAgainCounter++;
+          increaseThreadDepth = true;
+      }
 
       // MultiPV loop. We perform a full root search for each PV line
       for (pvIdx = 0; pvIdx < multiPV && !Threads.stop; ++pvIdx)