Fix errors in vtkUncertaintySurfacePainter.

Don't recompile and reinitiaze uniforms on every render. We just need to
do it during PrepareForRender is a new shader is being setup. Fixed
that. This overcomes OpenGL errors raised when sending the uniforms.

Change-Id: Idb7363a56a7187a6d5bac99e85f9a59b6de2277f
Merge topic 'lookup_table_cleanup' into next

5b201cf2 Fix errors in vtkUncertaintySurfacePainter.