fixed bug with special case of hip roof with 0-vector normalization
fixed bug with special case of hip roof with 0-vector normalization

markraz/vtp,nakijun/vtp,seanisom/vtp,markraz/vtp,seanisom/vtp,nakijun/vtp,seanisom/vtp,markraz/vtp,nakijun/vtp,seanisom/vtp,nakijun/vtp,markraz/vtp,seanisom/vtp,nakijun/vtp,markraz/vtp