Remove stream check from PackParticlesAndVertices
The check removed here is an optimisation to prevent work in the case of no objects to pack. It is being removed because it breaks a contract the algorithm makes: if the
AlwaysCreateOutput
and AlwaysCreateContainers
properties are set, the algorithm
should always create the specified containers. With the check in place, if the stream root
does not exist the locations will not to be created.