Drop to qsearch at low depth in razoring

If razoring conditions are satisfied and
depth is low, then directly drop in qsearch.

Passed both STC
LLR: 2.98 (-2.94,2.94) [-1.50,4.50]
Total: 12914 W: 2345 L: 2208 D: 8361

And LTC
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 50600 W: 7548 L: 7230 D: 35822

bench: 8739659

src/search.cpp

@@ -582,6 +582,10 @@ namespace {
  && abs(beta) < VALUE_MATE_IN_MAX_PLY
  && !pos.pawn_on_7th(pos.side_to_move()))
  {
+ if ( depth <= ONE_PLY
+ && eval + razor_margin(3 * ONE_PLY) <= alpha)
+ return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
+
  Value ralpha = alpha - razor_margin(depth);
  Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
  if (v <= ralpha)