Missing bones cause files to be unreadable externally

[RavenTheSergal]

Describe the bug 💬

I am exporting an unpacked prefab that has a missing bone or two. what i expect to happen is the group with a missing bone will be ignored, and the model will export normally. instead what happens is the missing bone is replaced with the next in the list, causing 2 issues.

1. in unity, the order of the bones is now incorrect, scrambling the parts.
2. other applications, like blender, cannot read the file due to an index mismatch

Steps to reproduce 🔢

1. use any rigged model
2. unpack the file
3. delete a bone
4. export

done, it should be messed up.

Files to reproduce the issue ♻

personal files unnecessary, i went and tested with several assets, all with the same result.

Editor Version 🎲

2022.3

Render Pipeline and version

Built in render pipeline

UnityGLTF Version

latest

Operating System 👩‍💻

Windows

When does this problem happen?

• [ ] Editor Import
• [ ] Runtime Import
• [x] Editor Export
• [ ] Runtime Export

Additional Info 📜

No response

Validations 🩹

• [x] I have searched existing issues: no issue already exist that reports the same problem.
• [x] I follow the Code of Conduct
• [x] I provided a minimal reproducible example, including files when necessary.