After razoring, IID, null verification and singular
extension searches we have could have a dirty ss->bestMove,
restore to MOVE_NONE before to enter moves loop.
This should avoid to store in TT a stale move when
we fail low.
Tested together with previous patch that is the
one that gives ELO.
After 1152 games at 1+0 on my QUAD
Mod vs Orig +233 =716 -203 (+9 ELO)
Signed-off-by: Marco Costalba <mcostalba@gmail.com>