Export selection with USD Export do not work if only a skeleton is selectedand it breaks any future export selection

**Describe the bug**
Hello!
There is an issue with "Export selection" when the only selected object is a joint. It even breaks the following export selections, even if you delete the joint and try to export the node only. The repro steps are simple and will give all the details needed.

**Steps to reproduce**
Steps to reproduce the behavior:
1. Open a new scene
2. Create an empty group
3. Create a joint and put it into the group like this
4. Select the joint
5. Go to File -> Export Selection
6. Choose the option "USD Export" for "Files of types:"
7. Click on export.
8. Notice a pop-up saying "Nothing is selected". The following picture show that the joint is clearly selected.
9. Delete the joint
10. Select the transform node "null1"
11. Do step 5 to 7, the pop-up is there again. Note that, if we do select null1 and export the selection *before* creating joint1, we can export. So, we seem to be stuck in a broken state when we first try to export the skeleton only.

**Expected behavior**
When selecting the root joint, the skeleton should be exported. Also, if it fails, it shouldn't break the scene for any future export selection.

**Attachments**
See repro steps

**Specs (if applicable):**
- OS & version Windows 10
- Maya version Maya 2023.3 and Maya 2022.4
- Maya USD 0.21.0 for Maya 2023, 0.20.0 for Maya 2022