COMP: Fix [[nodiscard]] warnings in PolyLineParametricPath1 example

Fixed Mac/Darwin Clang warnings saying:

> warning: ignoring return value of function declared with 'nodiscard' attribute [-Wunused-result]

From https://open.cdash.org/viewBuildError.php?type=1&buildid=8600267

Examples/DataRepresentation/Path/PolyLineParametricPath1.cxx

@@ -102,9 +102,15 @@ main(int argc, char * argv[])
   point[0] = origin[0] + spacing[0] * size[0];
   point[1] = origin[1] + spacing[1] * size[1];
 
-  image->TransformPhysicalPointToContinuousIndex(origin, cindex);
+  using ContinuousIndexValueType = ContinuousIndexType::ValueType;
+
+  cindex =
+    image->TransformPhysicalPointToContinuousIndex<ContinuousIndexValueType>(
+      origin);
   path->AddVertex(cindex);
-  image->TransformPhysicalPointToContinuousIndex(point, cindex);
+  cindex =
+    image->TransformPhysicalPointToContinuousIndex<ContinuousIndexValueType>(
+      point);
   path->AddVertex(cindex);
   // Software Guide : EndCodeSnippet