"ShowFlag.InstancedFoliage 0" hides HISMC

Hierarchical Instanced Static Mesh components that contain no foliage are disappearing when ShowFlag.InstancedFoliage 0 is used.

This was reported and tested in 4.24.3 (CL-11590370) and reproduced in 4.25.3 (CL-13942748).

1. Open the UE4 Editor and create a Blank project
2. Create an Actor Blueprint and add a Hierarchical Instanced Static Mesh component to it
3. Add a Cube to the HISMC and a few instances
4. Add the Blueprint to the Level, open the Console, and type ShowFlag.InstancedFoliage 0

Results: The HISMC will be hidden

Expected: HISMC that isn't grass will stay visible