Fix photon replicas generation + make vp-nextfitruncard use Q0 instead of Qmin for iterating preprocessing
Created by: niclaurenti
Opening this PR to fix a bug in the photon sector: in the case of single replica fits, after that the Photon object was computed in
it was recomputed in
with replicas=[1].
Since replicas is a list containing the replicas IDs of the different replicas, it was computing the replica n. 1 for all the replicas (sorry for repeating replicas 5 times in a single sentence).
Moreover, the Photon object already contains just one photon in the single replica fits, so there's no need to recompute it imposing just 1 replica.