FEM can't mesh a linked object

Issue imported from https://tracker.freecad.org/view.php?id=4568

* **Reporter:** Jee-Bee
* **Date submitted:** 2/15/2021
* **FreeCAD version:** 0.2
* **Category:** Bug
* **Status:** new
* **Tags:**

# Original report text

The FEM Mesh don't accept non-shaped objects.
The result is that linked bodies can't be used as input for creating a mesh.

# Additional information

see topic: https://forum.freecadweb.org/viewtopic.php?f=18&t=53372

# Steps to reproduce

n.a.

# Other bug information

* **Priority:** normal
* **Severity:** major
* **Category:** Bug
* **Updated:** 2/15/2021

Start by reproducing the FEM meshing workflow with a linked body, using the original report and the linked forum topic for context. No source file, test, or entry point is named; done means linked, non-shaped objects are accepted as mesh inputs without breaking existing FEM meshing.

Written by the indexing model from the issue text.