AST-831 Describe auto_*_sigma settings and use std::optional

cpp/radler.cc

@@ -210,10 +210,10 @@ void Radler::Perform(bool& reachedMajorThreshold, size_t majorIterationNr) {
   }
   if (_settings.auto_mask_sigma && !_autoMaskIsFinished)
     _parallelDeconvolution->SetThreshold(
-        std::max(stddev * *_settings.auto_mask_sigma, _settings.threshold));
+        std::max(stddev * (*_settings.auto_mask_sigma), _settings.threshold));
   else if (_settings.auto_threshold_sigma)
     _parallelDeconvolution->SetThreshold(std::max(
-        stddev * *_settings.auto_threshold_sigma, _settings.threshold));
+        stddev * (*_settings.auto_threshold_sigma), _settings.threshold));
   integrated.Reset();
 
   Logger::Debug << "Loading PSFs...\n";