Fix infinite recursion loop in truth helpers where truthparticle == truthparticle->parent()
2 truth-level helper functions are recursive and can cause infinite recursion when a truth particle is its own parent. This happens in some emerging jet exotic signal as mentionned in https://its.cern.ch/jira/browse/ATLASDPD-2052.
The proposed changes fix the crashes. I hope they make physical sense and that experts can confirm (@zmarshal do you know who else we can tag?)
If this MR is ok, we would ask it is added to a derivation release because the issue is currently preventing signal DPD production in our analysis.
Cheers, P-A