PR: Exporting curtain walls as IfcRailing: Regression in 25.4.3

### Problem Description

## 25.4.0 export behaviour
With the the 25.4.0 exporter we were able to export curtain walls as IfcRailing entities. Revit would export this (albeit as an aggregate) both for IFC2x3 and IFC4:

## 25.4.3 export behaviour
The 25.4.3 exporter shows a different behaviour.

### IFC2x3
For **IFC2x3** it **doesn't export a usable object**. In Solibri no entity is visible in the model structure:

In BIM Collab Zoom there is an entity visible in the model structure but it does not show any geometry:

### IFC4
No issues here. For IFC4 it now exports a single IfcRailing entity (no longer an aggregate) - for me personally that is an improvement (although it would generally be nice to be able to control on the type or instance level whether elemented objects are exported as aggregates or not).

### Revit Version

2025.4.x

### IFC for Revit Addon Version

25.4.0

### Windows Version

11 24H2

Start by reproducing the curtain-wall export with Revit 2025.4.x for IFC2x3 and compare the resulting model structure and geometry with the 25.4.0 behavior described here. Done means IFC2x3 exports a usable visible curtain-wall object, while the existing IFC4 behavior remains intact.

Written by the indexing model from the issue text.