Avoid an useless evaluate() call

Now that we have position static score we don't
need to call evaluate() a second time.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/search.cpp

@@ -1457,7 +1457,7 @@ namespace {
 
     // Go with internal iterative deepening if we don't have a TT move
     if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
-        !isCheck && evaluate(pos, ei, threadID) >= beta - IIDMargin)
+        !isCheck && ss[ply].eval >= beta - IIDMargin)
     {
         search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
         ttMove = ss[ply].pv[ply];