ActorPositionWS Material BP node can crash when used in Post Process material

The ActorPositionWS BP node calls GetActorWorldPosition() in HLSL which references Primitive.ActorWorldPosition. But GetActorWorldPosition() is not protected by an #if HAS_PRIMITIVE_UNIFORM_BUFFER check. This means it will compile even in cases when there is no primitive uniform buffer, and can lead to bad memory access.

NOTE: This was reported by a UDN user, and I did not reproduce the crash internally

To reproduce the dangerous material configuration:

create a new 3rd person blueprint project in UE4
select the floor actor
create a new material & open blueprint
add Coordinates -> ActorPositionWS
connect output pin to material's Emissive Color pin
change Material Domain to Post Process
-> this produces invalid configuration, but no error in stats