Fix consistency between PV and bestmove output

In case that a non-root mainThread on a node is the new best thread in the cluster, it should always output its PV.

src/cluster.cpp

@@ -58,8 +58,7 @@ static void BestMove(void* in, void* inout, int* len, MPI_Datatype* datatype) {
   MoveInfo* r = static_cast<MoveInfo*>(inout);
   for (int i=0; i < *len; ++i)
   {
-      if (    (l[i].depth > r[i].depth || (l[i].depth == r[i].depth && l[i].rank < r[i].rank))
-          && (l[i].score >= r[i].score))
+      if (l[i].depth >= r[i].depth && l[i].score >= r[i].score)
          r[i] = l[i];
   }
 }

src/search.cpp

@@ -297,7 +297,7 @@ void MainThread::search() {
 
   if (mi.rank == Cluster::rank()) {
       // Send again PV info if we have a new best thread
-      if (bestThread != this)
+      if (!Cluster::is_root() || bestThread != this)
           sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
 
       sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());