title: Meshlab alignment issue
body: <p>When I am trying to align two point clouds in meshlab, there is an error saying No successful arc among candidate Alignment arcs. And even though the point clouds after alignment can be seen in window, I cannot save it successfully. However I try, the ply file which I save always contains only the last layer, rather than all the layers. Dose the saving failure have something to do with the process error？ How can I overcome this error? I work on Ubuntu 18.04 version.</p>