Part: Can't drag more objects into a Part:Compound (if objects do not have a Shape)

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Problem description

If I have a Union in Part, I can drag more objects into it.

But this doesn't work for Compound. Dragging something into the compound has no effect.

This seems like an inconsistency.

### Full version info

```shell
OS: macOS 14.6.1
Word size of FreeCAD: 64-bit
Version: 0.22.0dev.38553 (Git)
Build type: Release
Branch: main
Hash: 59c1ccec3e6b70f56eeee8f94d361019b84bd850
Python 3.11.9, Qt 5.15.13, Coin 4.0.2, Vtk 9.2.6, OCC 7.7.2
Locale: English/United States (en_US) [ OS: C/Default (C) ]
Installed mods:
* Curves 0.6.44
```

### Subproject(s) affected?

Part

### Anything else?

_No response_

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct