Small tweaks to recent code changes

As a note, current 2 LMR conditions on stat score
could be simplified in a single line:

r -= ((ss->statScore >= 0) - ((ss-1)->statScore >= 0)) * ONE_PLY;

We keep them splitted in 2 "if" statements because are easier
to (immediately) read.

No functional change.

src/search.cpp

@@ -935,7 +935,7 @@ namespace {
               int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
 
               // Countermoves based pruning (~20 Elo)
-              if (   lmrDepth <= ((ss-1)->statScore > 0 ? 3 : 2)
+              if (   lmrDepth < 3 + ((ss-1)->statScore > 0)
                   && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
                   && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
                   continue;