"No skinned Spatial for joint" in GltfLoader.setupControls()

[stephengold]

Forum discussion: https://hub.jmonkeyengine.org/t/gltf-glb-animated-model/47617

To reproduce:

1. Download the model using the "Download 3D Model" and "GLB Converted format Texture size: 1k" buttons.
2. Load the model using:

assetManager.registerLoader(GlbLoader.class, "glb");
ModelKey modelKey = new ModelKey(assetPath);
assetManager.loadModel(modelKey);

With JME 3.7.0-alpha3.1, the model loads with a warning but no exceptions:

Apr 23, 2024 3:22:32 AM com.jme3.scene.plugins.gltf.GltfLoader setupControls
WARNING: No skinned Spatial for joint "Root_00" -- will skin the models root node!

The loaded model contains a SkinningControl but no AnimComposer. There ought to be an AnimComposer because the GLB file contains an animation.