Volumetric lightmap + stationary light has missing shadows

Primitives with the "Lightmap Type" set to "Force Volumetric" are not shadowed correctly.

Issue dates back to at least 4.27.2.

As a workaround, making FLightCacheInterface::GetStaticInteraction always return LIT_MAX for bGlobalVolumeLightmap looks to resolve most of the issues (except static geometry)

• Disable VSM with r.shadow.virtual.enable 0
• Add a sphere, set it's "lightmap type" to "force volumetric"
• Add a spotlight, set it to stationary. Point it at the sphere.
• Add a cube between the spotlight and the sphere. This will be the shadow-caster
• Build the lighting with Lightmass
• Observe that the sphere is not shadowed.