No faces or verts causes null error

[mflux]

How to reproduce:

Given a MeshA with 0 verts or faces Given a MeshB with some verts (say.. a THREE.CubeGeometry)

Do meshA.intersect( meshB )

Gives a null error at line 303 this.plane.flip()

chandlerp : if there's no faces, no build operation happens, which means the plane attribute remains null