minor fix in an assert in plane_project.cpp
minor fix in an assert in plane_project.cpp

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