Failure to restart: "Not running with stars but about to receive stars in proxies!"

I think I've found a small inconsistency with the cell_extra_sparts parameter. In runs without stars it gets forced to zero in space_init(). On restarting, the zero value gets read back in from the restart file but it is then overwritten with the value from the parameter file. If that is non-zero then Swift crashes in engine_allocate_foreign_particles() with "Not running with stars but about to receive stars in proxies!". It looks like this might affect space_extra_gparts and space_extra_sinks too.

I can reproduce the crash on the SmallCosmoVolume_Cooling if I add Scheduler:cell_extra_sparts=100 in the .yml file, generate a set of restart files, then try to restart from them (I only encountered this because I was using an old version of small_cosmo_volume.yml which still contained cell_extra_sparts).