message: Fix debug builds
diff: @@ -47,8 +47,8 @@ public:
  {
  // Require values to be sorted by wavelength
  assert(std::is_sorted(
  - values.begin(),
  - values.end(),
  + values_.begin(),
  + values_.end(),
  [](std::pair<float, float> a, std::pair<float, float> b)
  {
  return a.first < b.first;
  