Give a sensible DM softening also for runs without DM
Fix #656 (closed).
When running a baryon-only simulation, initialise the DM softening to the baryon softening since this is the one used by the basic gravity schemes.
Fix #656 (closed).
When running a baryon-only simulation, initialise the DM softening to the baryon softening since this is the one used by the basic gravity schemes.