FIX: promotion bug - undesired check

[dfeprado]

If a black king is sitting on row 8 and a paw is promoted to a bishop, and there's no piece between these two, the unfixed code would evaluate to a check situation. The following images show this

Initially, we have this situation:

After promoting the White H7 Pawn to a White H8 Bishop, the blacks would end in check:

But that's a bug! The White Bishop cannot check the Black King on that situation.

This commit fix this bug.