fixed compilation issue with libpng 1.4.x
fixed compilation issue with libpng 1.4.x

frangarcj/Genesis-Plus-GX,DavidKnight247/Genesis-Plus-GX,Oggom/Genesis-Plus-GX,DavidKnight247/Genesis-Plus-GX,DavidKnight247/Genesis-Plus-GX,Oggom/Genesis-Plus-GX,Oggom/Genesis-Plus-GX,frangarcj/Genesis-Plus-GX,Oggom/Genesis-Plus-GX,DavidKnight247/Genesis-Plus-GX,frangarcj/Genesis-Plus-GX,frangarcj/Genesis-Plus-GX