Can't assign LightMapCoordinateIndex on Static Mesh with generated LODs

Once a static mesh have generated LODS, the only lightmap index value the static mesh editor's UI accepts is 0.

We should be able to set the index to any value between 0 and 3 as long as there are valid UVs at that index.

1. In the editor, open up the static mesh editor on any static mesh with more than 1 UV.
2. Change the number of LOD in order to have generated LODS in your static mesh, apply.
3. Now try to change the "Light Map Coordinate Index", it will be stuck on index 0 even if you have valid UV at index 1.