How to reproduce:
1. Open the attached project
2. In the Project Window, select the "Avatar_Base"
3. Open the Sprite Editor (selected in the Inspector window)
4. In the Sprite Editor window, switch to the Skinning Editor
5. Create bones
6. Copy created bones
7. Paste them in any other sprite

Expected result: Bones are pasted and there are no errors
Actual result: Bones are not pasted and there is an IndexOutOfRangeException error thrown

Reproducible with: 3.2.10 (2019.4.29f1), 5.0.7 (2020.3.16f1), 6.0.5 (2021.1.17f1), 7.0.0-pre.3 (2021.2.0b7, 2022.1.0a5)

Note:
- Bone data is copied from a PSB file, doesn't seem to be reproducible with PNGs