COMP: Fix windows compilation warning

Modules\Filtering\LabelMap\include\itkShapeKeepNObjectsLabelMapFilter.h(156):

warning C4269: 'comparator': 'const' automatic data initialized with compiler generated default constructor produces unreliable results

Author: hjmjohnson

Modules/Filtering/LabelMap/include/itkShapeKeepNObjectsLabelMapFilter.h

@@ -153,12 +153,12 @@ class ITK_TEMPLATE_EXPORT ShapeKeepNObjectsLabelMapFilter : public InPlaceLabelM
       auto end = labelObjects.begin() + m_NumberOfObjects;
       if (m_ReverseOrdering)
       {
-        const Functor::LabelObjectReverseComparator<LabelObjectType, TAttributeAccessor> comparator;
+        const Functor::LabelObjectReverseComparator<LabelObjectType, TAttributeAccessor> comparator{};
         std::nth_element(labelObjects.begin(), end, labelObjects.end(), comparator);
       }
       else
       {
-        const Functor::LabelObjectComparator<LabelObjectType, TAttributeAccessor> comparator;
+        const Functor::LabelObjectComparator<LabelObjectType, TAttributeAccessor> comparator{};
         std::nth_element(labelObjects.begin(), end, labelObjects.end(), comparator);
       }
       progress.CompletedPixel();