Skinned model animation starts in T-pose for one frame

**Issue description:**

I'm spawning a prefab, with a single animated model as root. The model is a character imported in T-pose. It has an animgraph that always outputs a looping animation. When playing the game in the editor, the character is spawned, but it flickers from t-pose once on spawn, before it plays the animation normally

**Steps to reproduce:**

1. Import an animated model with looping animation.
2. Create a prefab with this model. Set the model as root and delete the empty.
3. Create an animgraph and drag the animation in it.
4. Connect the animation to the output.
5. Set the animgraph for the model in the prefab
6. Write a simple script that spawns the prefab over and over again to make it easy to spot. (included in the repro project)

**Minimal reproduction project:**

[TPoseBug.zip](https://github.com/FlaxEngine/FlaxEngine/files/13847958/TPoseBug.zip)

**Flax version:**

1.7.6407.2 (master on jan 06)

Open TPoseBug.zip and reproduce the spawn sequence described in the issue. Start by examining the prefab's root animated model and its animgraph, then trace initialization around the first spawned frame. Done means the model no longer visibly flickers into its imported T-pose before the looping animation plays.

Written by the indexing model from the issue text.