bug fix in double area
bug fix in double area

JianpingCAI/libigl,JianpingCAI/libigl,aaronzou/Shape-Deformation,aaronzou/Shape-Deformation,aaronzou/Shape-Deformation,JianpingCAI/libigl,JianpingCAI/libigl,JianpingCAI/libigl,aaronzou/Shape-Deformation,JianpingCAI/libigl,aaronzou/Shape-Deformation