Wrong attributes JOINTS_0 and WEIGHTS_0 on skin export, re-import graphical issue

[anonymous2585]

Describe the bug
I have an FBX file in my Unity asset containing a skin with only 2 bones:

When I export it, the glb produced has validation errors for attributes JOINT_0 and WEIGHTS_0:

Invalid accessor format '{VEC2, FLOAT}' for this attribute semantic. Must be one of ('{VEC4, FLOAT}', '{VEC4, UNSIGNED_BYTE normalized}', '{VEC4, UNSIGNED_SHORT normalized}').glTF Validator(MESH_PRIMITIVE_ATTRIBUTES_ACCESSOR_INVALID_FORMAT)

When the glb is re-imported as an asset with glTFast importer, the skin goes crazy:

To Reproduce
Steps to reproduce the behavior:

1. Add the FBX file in your project assets SkinIssue.zip
2. Place the model in an empty scene
3. Select the model root in hierarchy, and use menu "GameObject => Export glTF => glTF-Binary (.glb)"
4. Save the file in your project asset
5. See Unity internal error "Bone index is not within the number of bones."
6. Remove the FBX model from the scene and place the glb model in scene
7. See incorrect mesh rendering

Expected behavior
=> When exported, the glb JOINT_0 and WEIGHTS_0 point to accessors of type "VEC4".
=> When re-imported, the glb displays exactly as the source FBX

Desktop (please complete the following information):

• glTFast version 6.17.0
• Unity Editor version 6000.0.71f1

Additional context
The attribute dimension is 2 in this case, but glTF spec want it to be always exactly 4 bones, see glTF 2.0 spec chapter 3.7.3.3:

The number of joints that influence one vertex is limited to 4 per set, so the referenced accessors
MUST have VEC4 type and following component types [...]

It is needed to pad the attribute accessor during export, because this Unity mesh return accessors with only 2 dimension: