Fix for BUG0013829: vtkAssembly::GetBounds adds bounds which are unintialized.

BUG 0013829 (https://vtk.org/Bug/view.php?id=13829)

Even though the status of bug is fixed it wasn't completely fixed.
For some reason, the implementor of the fix didn't make this change.
This commit completes the bug fix by setting the prop as visible if at least one prop has a valid bounds.

Rendering/Core/vtkAssembly.cxx

@@ -369,7 +369,6 @@ double *vtkAssembly::GetBounds()
     vtkProp3D* prop3D = static_cast<vtkProp3D *>(path->GetLastNode()->GetViewProp());
     if (prop3D->GetVisibility() && prop3D->GetUseBounds())
     {
-      propVisible = 1;
       prop3D->PokeMatrix(path->GetLastNode()->GetMatrix());
       const double* bounds = prop3D->GetBounds();
       prop3D->PokeMatrix(nullptr);
@@ -379,6 +378,8 @@ double *vtkAssembly::GetBounds()
       {
         continue;
       }
+      // Only set the prop as visibile if atleast one prop has a valid bounds
+      propVisible = 1;
 
       double bbox[24];
       // fill out vertices of a bounding box