[vtkusers] Rendering XYZRGBA segfaults randomly while XYZ doesn't in qvtkwidget subclass

[Oon-Ee Ng]

Bump, anyone has comment? Obviously, if I record the stream to a bunch
of .pcd files and read from them, the qvtkwidget subclass works fine,
but I don't know enough about VTK's internals to try to debug what's
going on with memory.