Fix missing DWG imports in ArchSectionPlane.getSVG
Fix missing DWG imports in ArchSectionPlane.getSVG

When a DWG file is imported into FreeCAD it gets imported as a Part
object with a compound shape. One would imagine, that such an object
should be rendered like a symbol inside a TechDraw View. But when the
imported shape is inside a SectionPlane that also contains solids, the
shape is not included in the SVG.

The problem is, that getCutShapes only uses solid shapes, when a volume
was cut before. But the imported DWG is a flat 2D object and has no solids
inside.

To fix it, the getSVG method will check if an object looks like a draft
object, meaning:
 - It has a shape
 - It has no solids
 - It has no volume

When it finds such a shape, it will treat it like a draft object. So
it is displayed like a symbol in the resulting SVG.

https://forum.freecadweb.org/viewtopic.php?f=3&t=34079

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