mesh_segment_by_path silently drops mesh faces

[cornelmpop]

The function drops some faces that clearly should not be dropped. A reproducible example:

mesh <- demoSphere
pois <- t(demoSphere$vb)[c(1, 20, 30, 45), 1:3]
mesh_path <- sPathConnect(pois, mesh, closed = TRUE)
res <- mesh_segment_by_path(mesh, mesh.path = mesh_path)

#' No purple face from the un-split mesh should be visible, but one is because the split
#' mesh segments don't cover the whole surface (i.e., a face was dropped)
shade3d(mesh, col = "purple", alpha = 0.9)
shade3d(res[[1]], col = "red")
shade3d(res[[2]], col = "green")