Move entropy floor until after density drift

Previously the entropy floor (and entropy/energy) bounding was done before the floor bounding (as was the correction of the smooth pressure in pressure-based schemes that @lhausammann uses).

This has been corrected.

This change makes no difference to galaxy properties with the SPHENIX scheme.

@lhausammann it may be worth checking your GEAR simulations to see if this changes anything as I know you use P-U.