Polyline does not clear mesh when point count <2

I was writing a quick and dirty polyline animator and noticed that when the point count is < 2 the line mesh is not actually cleared, persisting the mesh that was last generated for the polyline when its point count was >= 2.

I took a look at the `GenPolylineMesh` function and while it clears the managed mesh data, it returns early when point count is <2, before assigning to the mesh.

I was able to work around this by manually calling `polyline.Mesh.Clear();` but wanted to call it out!