Do not overwrite valuable TT data after probcut.

This patch allows an engine to write probcut data only in case
the probcut search depth is greater than transposition table depth.

passed STC
https://tests.stockfishchess.org/tests/view/5f0b52e959f6f035328949a6
LLR: 2.97 (-2.94,2.94) {-0.50,1.50}
Total: 52544 W: 10145 L: 9880 D: 32519
Ptnml(0-2): 853, 6097, 12121, 6334, 867

passed LTC
https://tests.stockfishchess.org/tests/view/5f0bd94c59f6f035328949f3
LLR: 2.93 (-2.94,2.94) {0.25,1.75}
Total: 49576 W: 6164 L: 5863 D: 37549
Ptnml(0-2): 297, 4371, 15218, 4538, 364

closes #2815

bench 4578298

src/search.cpp

@@ -925,9 +925,12 @@ namespace {
 
                 if (value >= probcutBeta)
                 {
-                    tte->save(posKey, value_to_tt(value, ss->ply), ttPv,
-                        BOUND_LOWER,
-                        depth - 3, move, ss->staticEval);
+                    if ( !(ttHit
+                       && tte->depth() >= depth - 3
+                       && ttValue != VALUE_NONE))
+                        tte->save(posKey, value_to_tt(value, ss->ply), ttPv,
+                            BOUND_LOWER,
+                            depth - 3, move, ss->staticEval);
                     return value;
                 }
             }