PositionAt/LocationAt returning wrong coordinates for edges of imported Dxf/Step curves

The case below tries to get the center point of the selected edge (in green), yet the returned position seems to be in some random place outside the edge/curve (orange dot).

I'd expect `locationAt`/`positionAt` to also function for imported curves/geometry.

When using `wires()` instead of `edges(..)`, the position returned by `positionAt`/`locationAt` is actually on the curve again - but that is a different use case.

I've added `start_point`/`end_point` just to test whether at least that data is available (yellow dots).

Curve used in the example case: [issue.zip](https://github.com/CadQuery/cadquery/files/6131882/issue.zip)

```python
curve = cq.importers.importDXF("issue.dxf").edges(">Y")
show_object(curve, options={"color":(100, 255, 0)})

t = curve.val().positionAt(0.5)
point = cq.Vertex.makeVertex(t.x, t.y, t.z)
show_object(point, options={"color":(255, 165, 0)})

start_point = curve.val().startPoint()
show_object(cq.Vertex.makeVertex(start_point.x, start_point.y, start_point.z))

end_point = curve.val().endPoint()
show_object(cq.Vertex.makeVertex(end_point.x, end_point.y, end_point.z))
```