fix: protect TrackSelector against eta=nan (#3785)

Protect against η=`nan` in `Acts::TrackSelector::isValidTrack()`, which would `throw std::invalid_argument{"Eta is outside the abs eta bin edges"}` exception. This can come about if somehow the track θ<0 or θ>π. We should try to prevent these out-of-range values, but having them shouldn't raise an exception.

Co-authored-by: Paul Gessinger <1058585+paulgessinger@users.noreply.github.com>

Core/include/Acts/TrackFinding/CombinatorialKalmanFilter.hpp

@@ -399,7 +399,7 @@ class CombinatorialKalmanFilter {
               measurementSelector(trackStateCandidates, isOutlier, logger);
       if (!selectorResult.ok()) {
         ACTS_ERROR("Selection of calibrated measurements failed: "
-                   << selectorResult.error());
+                   << selectorResult.error().message());
         resultTrackStateList =
             ResultTrackStateList::failure(selectorResult.error());
       } else {

Core/include/Acts/TrackFinding/TrackSelector.hpp

@@ -427,8 +427,9 @@ bool TrackSelector::isValidTrack(const track_proxy_t& track) const {
 
   const Config* cutsPtr{nullptr};
   if (!m_isUnbinned) {
-    if (absEta() < m_cfg.absEtaEdges.front() ||
-        _absEta >= m_cfg.absEtaEdges.back()) {
+    // return false if |eta| is outside its range, or nan.
+    if (!(absEta() >= m_cfg.absEtaEdges.front() &&
+          _absEta < m_cfg.absEtaEdges.back())) {
       return false;
     }
     cutsPtr = &m_cfg.getCuts(_eta);

Core/src/TrackFinding/MeasurementSelector.cpp

@@ -29,6 +29,11 @@ MeasurementSelector::MeasurementSelector(const MeasurementSelectorCuts& cuts)
     : MeasurementSelector({{GeometryIdentifier(), cuts}}) {}
 
 MeasurementSelector::MeasurementSelector(const Config& config) {
+  if (config.empty()) {
+    throw std::invalid_argument(
+        "MeasurementSelector: Configuration must not be empty");
+  }
+
   std::vector<InternalConfig::InputElement> tmp;
   tmp.reserve(config.size());
   for (std::size_t i = 0; i < config.size(); ++i) {