BUG: Check if calculator is proper type

Use the VerifyPreconditions method to check that the calculator is set
( in the base class ) and that it is a OtsuThresholdCalculator is the
OtsuThresholdImageFilter class.

Author: blowekamp

Modules/Filtering/Thresholding/include/itkHistogramThresholdImageFilter.h

@@ -197,6 +197,17 @@ class ITK_TEMPLATE_EXPORT HistogramThresholdImageFilter : public ImageToImageFil
   void
   GenerateData() override;
 
+
+  void
+  VerifyPreconditions() ITKv5_CONST override
+  {
+    Superclass::VerifyPreconditions();
+    if (m_Calculator.IsNull())
+    {
+      itkExceptionMacro(<< "No threshold calculator set.");
+    }
+  }
+
 private:
   OutputPixelType   m_InsideValue;
   OutputPixelType   m_OutsideValue;

Modules/Filtering/Thresholding/include/itkHistogramThresholdImageFilter.hxx

@@ -59,10 +59,6 @@ template <typename TInputImage, typename TOutputImage, typename TMaskImage>
 void
 HistogramThresholdImageFilter<TInputImage, TOutputImage, TMaskImage>::GenerateData()
 {
-  if (m_Calculator.IsNull())
-  {
-    itkExceptionMacro(<< "No threshold calculator set.");
-  }
   typename ProgressAccumulator::Pointer progress = ProgressAccumulator::New();
   progress->SetMiniPipelineFilter(this);
 

Modules/Filtering/Thresholding/include/itkOtsuThresholdImageFilter.h

@@ -118,6 +118,17 @@ class OtsuThresholdImageFilter : public HistogramThresholdImageFilter<TInputImag
     this->Superclass::GenerateData();
   }
 
+  void
+  VerifyPreconditions() ITKv5_CONST override
+  {
+    Superclass::VerifyPreconditions();
+    if (dynamic_cast<const CalculatorType *>(Superclass::GetCalculator()) == nullptr)
+    {
+      itkExceptionMacro(<< "Invalid OtsuThresholdCalculator.");
+    }
+  }
+
+
 private:
 #if defined(ITKV4_COMPATIBILITY)
   bool m_ReturnBinMidpoint{ true };