Fix final snapshot properties

The final dump of stats/snapshot/VR should have a drift but not a drift that initialises the particles. This was triggered by the jenkins suite.

@jborrow somehow, we never caught that the final snapshot had wrong values for things that get initialised in the drift and hence zeroed. Like the densities. Is that really true? Now that the default is SPHENIX, the code is actually crashing on the final dump as we try to gather entropies in the stats and this leads to a division by 0. Did we always have garbage densities in the final snapshots (not with an output list) or does that occur only if we use a fixed number of steps (-n)?

added SPH bug labels

This is quite concerning. I don't know why we haven't picked up on this before; do you have any idea why this didn't occur before? Surely we can't have always crashed on the final dump or we'd never get a z=0 snapshot.

I think the issue wasn't there with output lists or when running without -n X

Do we not dump on the final step for hydro tests too?

It must only be for -n X, I think. I'll take a look and try to verify that.

yeah but we don't divide by 0 density when using an entropy-based scheme which is what the old default was.

My point was that the scripts have been working for SPHENIX when I ran the code for hydro tests, so I hope it's not that.

I have not checked the snapshots but it's the stats collection of entropy that breaks.

Can repro this when using -n but not for non-step-limited runs using the SodShock. Cannot repro using cosmological runs for the statistics when using an output list (for the snapshots at least).

I have also tried running a sodshock with no snapshot outputs. In this case the statistics.txt file is fine (so it's not the case that outputting a snapshot on that step 'fixes' the problem).

So I guess the only case where this actually causes a problem is when we invoke with -n (thankfully)?

The alternative would be to not write a final stats file or snapshot file when ending a run with -n X since this is not a physical option anyway.

closed

Done in b1bc549a.

It's already merged but please shout if you disagree.