Check for easy move just once

Here the rational seems to be that if after one try easy
move detection fails then the easy move is not so easy :-)

After 15563 games at 60+0.05
ELO: 3.04 +-5.5 (95%) LOS: 97.0%
Total: 15563 W: 2664 L: 2528 D: 10371

No functional change.

src/search.cpp

@@ -293,6 +293,7 @@ namespace {
     Stack ss[MAX_PLY_PLUS_2];
     int depth, prevBestMoveChanges;
     Value bestValue, alpha, beta, delta;
+    bool triedEasyMove = false;
 
     memset(ss, 0, 4 * sizeof(Stack));
     depth = BestMoveChanges = 0;
@@ -439,10 +440,12 @@ namespace {
             // Stop search early if one move seems to be much better than others
             if (    depth >= 12
                 && !stop
+                && !triedEasyMove
                 &&  PVSize == 1
                 && (   RootMoves.size() == 1
                     || Time::now() - SearchTime > (TimeMgr.available_time() * 20) / 100))
             {
+                triedEasyMove = true;
                 Value rBeta = bestValue - 2 * PawnValueMg;
                 (ss+1)->excludedMove = RootMoves[0].pv[0];
                 (ss+1)->skipNullMove = true;