Fixes a segfault in vtkVRMLImporter after destructor called

Updates VTK to the current master to include this change.

Change-Id: If0d93366a1350f2cffc9fe38a5103ed3f8d0f7a3
Merge topic 'fix_vrml_importer_segfault' into next

5f026cab Fixes a segfault in vtkVRMLImporter after destructor called