OBJLoader: Better support point clouds.

[Mugen87]

Related issue: -

Description

I've lately encountered an OBJ file that could be loaded in Blender but not by OBJLoader. The file represented a point cloud but without defining a p element. So the file had only lines like:

v -0.050206 1.680299 -0.120761 0.545098 0.345098 0.266667

OBJLoader did already parse this file but the builder logic ignored it because of the missing p element. The PR enhances the loader with an additional if statement that enables the detection of such point cloud data.

[mrdoob]

Thanks!