Skip the case where the jet.p4 is scaled with zero.

This is needed to protect against the case when the (matched) gen jet pt is larger enough than the reco jet pt, causing the ‘ptscale’ to be set to zero and leading to a ZeroDivisionError further in the leptonMVA.py and ntupleTupes.py where the ‘jetPtRatio’ variable used for the leptonMVA training is set.