Fix bounds of FutilityMoveCounts

This is a left-over from ONE_PLY == 2.

No functional change.

Resolves #107
Profile Build with Hash=16

16MB for 1" searches is more comensurate with the average use case.

And 16 is the default used by stockfish bench, so it makes sense to be
consistent, if only to have the same minimum memory requirement for using
SF and compiling it with PGO.

No functional change.

Resolves #109