Extract a reliable PV line

Truncate the extracted PV from the point where
the score stored in hash starts to deviate from
the root score.

Idea from Ronald de Man.

bench: 8732553

src/search.cpp

@@ -1401,6 +1401,7 @@ void RootMove::extract_pv_from_tt(Position& pos) {
  const TTEntry* tte;
  int ply = 0;
  Move m = pv[0];
+ Value expectedScore = score;
 
  pv.clear();
 
@@ -1411,8 +1412,10 @@ void RootMove::extract_pv_from_tt(Position& pos) {
 
  pos.do_move(pv[ply++], *st++);
  tte = TT.probe(pos.key());
+ expectedScore = -expectedScore;
 
  } while ( tte
+ && expectedScore == value_from_tt(tte->value(), ply)
  && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
  && pos.legal(m, pos.pinned_pieces(pos.side_to_move()))
  && ply < MAX_PLY