No animations for animated models

[tellypresence]

On branch rendermesh-refactor or dev

For animated model BrainStem.usdz, value of render_scene.animations.size() is 0. Expectation is there should be at least 1 animation for this model:

For animated model CesiumMan.usdz, value of render_scene.animations.size() is 0. Expectation is there should be at least 1 animation for this model:

[syoyo]

#148