better fix (7074281)
No need to pollute the TT. Simply retreive the PV after 'best' and insert best in front.

10k games in 10"+0.1", against fa07e4c43e21ac3ab1eda5b6c4539355235761df
Score of ./chess/pv vs ./chess/master: 2782 - 2732 - 4486  [0.502] 10000

Good surprise:
* no regression
* stability is preserved, played 10k games without a crash or timeloss (read_pv() and write_pv() should crash with illegal hash moves)