Fix MVV/LVA move ordering
Fix MVV/LVA move ordering

_compareMovesMvvLva() was basing its comparisons off the raw difference
between attacker and victim value, which isn't proper MVV/LVA.

The method now first considers victim value, and attacker value only
if victim values are the same.

GunshipPenguin/shallow-blue,GunshipPenguin/shallow-blue,GunshipPenguin/shallow-blue,GunshipPenguin/shallow-blue