search: fix a bug and clear history update

search: fix a bug and clear history update

When a move produces a beta-cut off is marked as
success in history and all the remaining ones are
marked as failures.

The loop across the searched moves, that is used
to register failures, does not skip the good one,
that is then registered as a failure too.

The patch fixes the bug and cleanup the code.

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