fix bug using "trace outlines" for reprsentation in ifc2x3

Mentioned in #4593

The error message was (it was trying to access curves from the original mesh instead of dummy curve object):
```
Error: Python: Traceback (most recent call last):
  File "\blenderbim\bim\module\geometry\operator.py", line 46, in execute
    IfcStore.execute_ifc_operator(self, context)
  File "\blenderbim\bim\ifc.py", line 349, in execute_ifc_operator
    result = getattr(operator, "_execute")(context)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\blenderbim\bim\module\geometry\operator.py", line 169, in _execute
    core.add_representation(
  File "\blenderbim\core\geometry.py", line 52, in add_representation
    representation = ifc.run(
                     ^^^^^^^^
  File "\blenderbim\tool\ifc.py", line 34, in run
    return ifcopenshell.api.run(command, IfcStore.get_file(), **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\blenderbim\libs\site\packages\ifcopenshell\api\__init__.py", line 172, in run
    result = usecase_class(ifc_file, **settings).execute()
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\blenderbim\libs\site\packages\ifcopenshell\api\geometry\add_representation.py", line 73, in execute
    return self.create_plan_representation()
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\blenderbim\libs\site\packages\ifcopenshell\api\geometry\add_representation.py", line 170, in create_plan_representation
    return self.create_annotation2d_representation()
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\blenderbim\libs\site\packages\ifcopenshell\api\geometry\add_representation.py", line 833, in create_annotation2d_representation
    items = [self.file.createIfcGeometricCurveSet(self.create_curves(is_2d=True))]
                                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\blenderbim\libs\site\packages\ifcopenshell\api\geometry\add_representation.py", line 492, in create_curves
    curves = self.create_curves_from_curve_ifc2x3(is_2d=is_2d, curve_object_data=dummy.data)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\blenderbim\libs\site\packages\ifcopenshell\api\geometry\add_representation.py", line 575, in create_curves_from_curve_ifc2x3
    for spline in self.settings["geometry"].splines:
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'Mesh' object has no attribute 'splines'
```

src/ifcopenshell-python/ifcopenshell/api/geometry/add_representation.py

@@ -572,7 +572,7 @@ def create_curves_from_curve_ifc2x3(self, is_2d=False, curve_object_data=None):
             curve_object_data = self.settings["geometry"]
         dim = (lambda v: v.xy) if is_2d else (lambda v: v.xyz)
         results = []
-        for spline in self.settings["geometry"].splines:
+        for spline in curve_object_data.splines:
             points = spline.bezier_points[:] + spline.points[:]
             if spline.use_cyclic_u:
                 points.append(points[0])