Setting the respective Nanite FallbackTarget for given Fallback Values

[JanLoehr]

When I use either "unreal_nanite_percent_triangles" or "unreal_nanite_fallback_relative_error" to specify the parameters for the Nanite fallback mesh - in my case to give the collision a higher resolution - those values are still ignored in unreal because the FallbackTarget remains on "Auto". I guess it's safe to asssume, that if one of the two attributes is set, that it is desired to use the apropriate method as the FallbackTarget as well.