Fix bug with status code handling differences between Powheg and BcVegPy/GenXicc
In process of incorporating Powheg, change to deal with particle status codes was introduced for events passed through LHA to Pythia8 which interferes with BcVegPy and GenXicc generators. The issue is code at !577 (diffs) and as a result, for BcVegPy and GenXicc, not all events will be properly decayed as signal and potentially cuts are not applied correctly. This was first introduced in Gauss v56r8. Here I fixed this in most trivial way by checking generator from GenFSR which is already filled and if it is BcVegPy or GenXicc do not touch status codes.