FBXLoader error when loaded 1 frame animation

[solinehayes]

Description

When loading a FBX containing an animation with only one frame. We get an error
Example: The Boss.zip

Linked to this PR: #27057

Reproduction steps

1. Open threeJs editor of this PR: https://rawcdn.githack.com/solinehayes/three.js/issue27056-fixRotationDiscontinuities/editor/index.html
2. Import test character

Code

N/A

Live example

https://rawcdn.githack.com/solinehayes/three.js/issue27056-fixRotationDiscontinuities/editor/index.html

Screenshots

Version

r159 to be

Device

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Browser

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OS

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