Tweak statScore condition

The first change (ss->statScore >= 0) does nothing.

The second change ((ss-1)->statScore >= 0 ) has a massive change.
(ss-1)->statScore is not set until (ss-1) begins to apply LMR to moves.
So we now increase the reduction for bad quiets when our opponent is
running through the first captures and the hash move.

STC
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 57762 W: 10533 L: 10181 D: 37048

LTC
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 19973 W: 2662 L: 2480 D: 14831

Bench: 5037819

src/search.cpp

@@ -979,10 +979,10 @@ namespace {
                              - 4000;
 
               // Decrease/increase reduction by comparing opponent's stat score
-              if (ss->statScore > 0 && (ss-1)->statScore < 0)
+              if (ss->statScore >= 0 && (ss-1)->statScore < 0)
                   r -= ONE_PLY;
 
-              else if (ss->statScore < 0 && (ss-1)->statScore > 0)
+              else if ((ss-1)->statScore >= 0 && ss->statScore < 0)
                   r += ONE_PLY;
 
               // Decrease/increase reduction for moves with a good/bad history