CPAlgorithms: handle missing inputs in ParticleLevelOverlapRemovalAlg

This should give appropriate protection to missing input containers in the CP::ParticleLevelOverlapRemovalAlg. Note that the jet collection is for now always expected, because it's with respect to it that the overlap removal is done, though we may revisit this in the future if there's a need to support extended overlap removal strategies.

PhysicsAnalysis/Algorithms/TruthParticleLevelAnalysisAlgorithms/Root/ParticleLevelOverlapRemovalAlg.cxx

@@ -15,7+15,7 @@
 
 StatusCode ParticleLevelOverlapRemovalAlg::initialize() {
 
   ANA_CHECK(m_jetsKey.initialize());
   ANA_CHECK(m_electronsKey.initialize(SG::AllowEmpty));
   ANA_CHECK(m_muonsKey.initialize(SG::AllowEmpty));
   ANA_CHECK(m_photonsKey.initialize(SG::AllowEmpty));
@@ -26,7+26,7 @@
     m_decORmuon = m_muonsKey.key() + "." + m_decLabelOR.value();
   if (!m_photonsKey.empty())
     m_decORphoton = m_photonsKey.key() + "." + m_decLabelOR.value();
-  if (!m_jetsKey.empty())
-    m_decORjet = m_jetsKey.key() + "." + m_decLabelOR.value();
+  m_decORjet = m_jetsKey.key() + "." + m_decLabelOR.value();
 
   ANA_CHECK(m_decORelectron.initialize(SG::AllowEmpty));
   ANA_CHECK(m_decORmuon.initialize(SG::AllowEmpty));