Origin "unset" in FilterGenInTime module

[henrylay97]

I've noticed whilst analysing a set of files simulated as "intime cosmics" using this module in the generation stage that the origin field becomes set as unknown, as does the generator information. This is because when the MCTruth is remade in this module the default constructor is used and then these fields are not updated.

It is complicated by the fact that this module has the capacity to narrow multiple MCTruths into 1, so deciding what to set for these values could be non-trivial. In the SBND case this module is used to convert 1 MCTruth into 2 (out of time and intime), as such both could easily have these fields set to the same value as the original.

It appears from some of the hardcoding (e.g. here) that this would be true for all uses of this module across any experiment but I can't be certain. One solution could be to set the Origin & GeneratorInfo only in the scenario where they are identical for all inputted MCTruths? This would cover the main (only?) use of this module but in theory protect against false information being filled for the narrowing case.

I hope this makes some sense, I would be interested in hearing opinions from @wesketchum @lgarren @knoepfel before I proceed.