TechDraw: Problems with makeCosmeticLine3D while adding a line with Z extension

### Problem description

Using TechDraw to display a section of a view, along Z axe.
The section is in perspective to view the Z extend.
When using makeCosmeticLine3D, the extend in Z is not drawn and if the line is strictly vertical: "Base.FreeCADError: Unknown C++ exception".
If the section is not perspective, the Z extension cannot be seen but the crash remains.

### Workbench affected?

TechDraw

### Steps to reproduce

Open my example file
type in

[CrashCosm3Dw20230729.FCStd.gz](https://github.com/user-attachments/files/30590346/CrashCosm3Dw20230729.FCStd.gz)

Python console:
App.activeDocument().getObject("SectionView010").makeCosmeticLine3D(App.activeDocument().getObject("Line").Start,App.activeDocument().getObject("Line").End)

### Expected behavior

A vertical cosmetic line should be drawn in then perspective section view, with the Z coordinates correct.

### Actual behavior

With the vertical line supplied (with same X,Y) makeCosmeticLine3D crash with "Base.FreeCADError: Unknown C++ exception"
If you change a little X or Y of line.End, an horizontal line is drawn, ignoring the Z extention.

### Development version About Info (in Safe Mode)

```shell
Reproduces with the latest weekly:

OS: Linux Mint 22.3 Cinnamon (X-Cinnamon/cinnamon/xcb)
Architecture: x86_64
Version: 26.3.0dev.20260728 (Git shallow) AppImage
Build date: 2026/07/28 21:59:12
Build type: Release
Branch: (HEAD detached at 63af5cb2f)
Hash: 63af5cb2f3dbb2b4c7333f6d220b03e05bf92f99
Python 3.11.14, Qt 6.8.3, Coin 4.0.10 (bundled), Pivy 0.6.11 (bundled), Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, Clipper2 , IfcOpenShell 0.8.0, OCC 7.8.1
Locale: French/France (fr_FR)
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Light/
QPA/File dialog/Color dialog: xcb/via Qt/via Qt
Navigation Style/Orbit Style/Rotation Mode: Gesture/Rounded Arcball/Window center
Logical DPI/Physical DPI/Pixel Ratio: 96/81.5973/1
OpenGL version/vendor/renderer: 4.6 (Compatibility Profile) Mesa 25.2.8-0ubuntu0.24.04.2/Intel/Mesa Intel(R) Graphics (RKL GT1)
```

### Last known good version (optional)

```shell

```

Reproduce the crash with CrashCosm3Dw20230729.FCStd.gz, then run the supplied Python-console call to SectionView010.makeCosmeticLine3D using the Line object's Start and End points. Inspect the makeCosmeticLine3D entry point and determine why vertical points and Z extension are mishandled. Done means a vertical cosmetic line renders in perspective with correct Z coordinates and no exception.

Written by the indexing model from the issue text.