Fix truth handling in InDetPhysValMonitoring tool with hard scatter flag set
This MR prevents the InDetPhysValMonitoringTool::getTruthParticles()
method from bailing out whenever a truth option not equal to All
is set.
It also adds logic to catch invalid links when populating the hard scatter truth vector.
This MR is required for the ID tracking ART and physics validation to work properly. Adding @nicolaid and @npetters for information. This MR is needed to get useful PhysVal results for tracking. Adding urgent label due to upcoming intermediate PhysVal.