Niagara Parameter Collection Overrides aren't working

Parameter collection overrides defined in the Niagara system's System Properties do not work.

In FNiagaraSystemSimulation::GetParameterCollectionInstance the return value of GetParameterCollectionOverride is not stored, so the overrides are never used.

1. Create a Niagara System based on the Fountain emitter
2. Create a Niagara Parameter Collection
3. Add a float parameter, and set its value to 100
4. Link the Emitter's spawn rate to the float parameter from step 3 
5. Create a Niagara Parameter Collection Instance 
6. Set the Parameter Collection Instance's Collection to the collection from step 2
7. Override the float parameter in the collection instance by checking the box next to it
8. Expand the parameter's properties by clicking the expand arrow
9. In the expanded field set the float's value to 0.0 and save the collection instance
10. In the Niagara system's System Properties module add an entry to Parameter Collection Overrides
11. Set the override to the collection instance from step 5
12. Save and compile the system

RESULT

The emitter still spawns particles, even though it should have a spawn rate of 0.0