BUG: Fix vtkMRMLDiffusionWeightedVolumeDisplayNode pipeline

Issue #3514

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23124 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Fix crash in vtkMRMLModelDisplayableManager

Regression from r23118

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23125 3bd1e089-480b-0410-8dfb-8563597acbee