[AI] Navmesh does not generate correctly on a negatively scaled ISM.

Setting a single axis of an ISM negative results in navmesh not being generated on top of it. However, setting 2 axes to negative scale does have the navmesh generate as is expected. 

Also see more information in this second thread:

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1. Add an empty actor to a scene
2. Add an InstancedStaticMeshComponent to the newly placed actor
3. Add mesh and an instance in ISM component.
4. Make the scale of the ISM large enough for navmesh to generate on top of (a value of 2 works with the default cube)
5. Scale ISM negatively on a single axis

Expected Result: Navmesh is generated on top of the ISM

Actual Result: Navmesh is not generated on top of the ISM