Reset search time as early as possible

In particualr before to wake up main thread that
could take some random time. Until we don't reset
search time we are not able to correctly track
the elapsed search time and this can be dangerous
under extreme time pressure.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/thread.cpp

@@ -432,6 +432,8 @@ void ThreadsManager::start_searching(const Position& pos, const LimitsType& limi
                                      const std::set<Move>& searchMoves) {
   wait_for_search_finished();
 
+  SearchTime.restart(); // As early as possible
+
   Signals.stopOnPonderhit = Signals.firstRootMove = false;
   Signals.stop = Signals.failedLowAtRoot = false;