Improve 3D DXF import/error handling (currently imports as blank document)

Steps to reproduce:

• open Inkscape
• Import a 3D dxf

What happened?

A new empty paper appear

What should have happened?

One of these:

• the topview of the content apear
• Inkscape ask for the orientation Please chose an orientation xy/yz/zx [preview]
• A popup appera Could not import 3D-DXF data. Because this file do not contain other data, Nothing was imported
• DXF has a not suported Version. We could only open DXF Version XX this File has version XX

Inkscape Version and Operating System:

• Inkscape Version: 1.0beta2 (f3d5b5a, 2020-03-13)
• Operating System: Windows 10

Please chose: I could generate Example files as complex and in Versions you like, with and without 3D Body/other (Model and Paper): DXF or DWG Verion: R12/R13/R14/R2000-2002/R2004-2006/R2010/R2013/R2018