[BUG] Accessors with sparse storage but without bufferView fail validation

[seberoth]

Describe the bug
If a accessor uses sparse storage but hasn't defined a bufferView, the validation fails with Message: Accessor[13] _bufferView: must be defined.
The gltf spec says thats allowed but the accessor MUST be initialized with zeros.

GLTF 2.0 Accessor specs

To Reproduce
Example glb file is attached

please complete the following information:

• OS: Windows 11
• SharpGLTF Version: 1.0.0-alpha0030

example accessor

    {
      "componentType": 5126,
      "count": 7251,
      "sparse": {
        "count": 5920,
        "indices": {
          "bufferView": 13,
          "componentType": 5123
        },
        "values": {
          "bufferView": 14
        }
      },
      "type": "VEC3"
    }

a0_005_ma__strongarms_int_l.zip

EDIT: Probably related Blender GLTF plugin commit: KhronosGroup/glTF-Blender-IO@9ea179a

[vpenades]

Yes, this is a known issue; for some reason I don't undersand (and I don't fully agree) Khronos accepts glTF with missing buffers as valid.

The problem is that supporting missing buffers breaks some stuff inside the APIs, so I am still reasearching for a proper solution.

[vpenades]

I recalled I already asked about this issue here KhronosGroup/glTF-Validator#189

I'll investigate a solution...