fix display of cylinder

src/Vtk/uLibVtkInterface.cxx

@@ -121,6 +121,7 @@ public:
     TRS m_Transform;
 
     void ApplyAppearance(vtkProp *p) {
+        if (!p) return;
         p->SetVisibility(m_Visibility);
         p->SetPickable(m_Selectable);
         p->SetDragable(m_Dragable);
@@ -143,6 +144,13 @@ public:
             if (m_Opacity != -1.0) {
                 actor->GetProperty()->SetOpacity(m_Opacity);
             }
+        } else if (vtkAssembly *asm_p = vtkAssembly::SafeDownCast(p)) {
+            // Recursively apply to parts of the assembly
+            vtkProp3DCollection *parts = asm_p->GetParts();
+            parts->InitTraversal();
+            for (int i = 0; i < parts->GetNumberOfItems(); ++i) {
+                this->ApplyAppearance(parts->GetNextProp3D());
+            }
         }
     }