add protection for missing handleExtResults

Author: gouskos

PhysicsTools/NanoAOD/plugins/L1TriggerResultsConverter.cc

@@ -135,7 +135,9 @@ void L1TriggerResultsConverter::produce(edm::Event& iEvent, const edm::EventSetu
     if (store_unprefireable_bit_) {
       edm::Handle<GlobalExtBlkBxCollection> handleExtResults;
       iEvent.getByToken(token_ext_, handleExtResults);
-      unprefireable_bit = handleExtResults->at(0, 0).getExternalDecision(GlobalExtBlk::maxExternalConditions - 1);
+      if (handleExtResults->size() != 0) {
+	unprefireable_bit = handleExtResults->at(0, 0).getExternalDecision(GlobalExtBlk::maxExternalConditions - 1);
+      }
     }
   } else {
     // Legacy access