Crash on reimport animation when there is an additive animation track and fbx frame number is different

When an animation sequence has an additive animation track, reimporting a fbx would crash the editor if the new fbx has a different number of frames.

1. Import anim.fbx in anim1 folder, make sure to import animation and set Default Sample Rate on
2. Add the imported animation an additive animation track(select a bone and add a key)
3. Override the original anim.fbx with another anim.fbx in anim2 folder
4. From the context menu of the animation(anim_Anim), click reimport