Using mask_points option in mlab.points3d crashes python

Plotting a list of points with `points3d(x,y,z)` works fine. Trying to plot the same points with the `mask_points` option gives a segfault.

This can be recreated within the gui by editing the pipeline. Clicking on Glyph->Glyph->Masking->"Mask input points" has the same effect.