surface fluxes without layers
Currently, when there are no layers left (ie simulation without soil and no more snow), the surface fluxes (for example Sdata.qs) will be printed out with wrong values (often a few thousands).
In order to improve these outputs, we should set the fluxes to nodata (or undefined) in SurfaceFluxes::collectSurfaceFluxes() and properly handle the averaging that happens later.