message: Make dist-threshold default to double max in distributed distance quesry example.
  Also check that the input value is non-negative.
diff: // C/C++ includes
  #include <string>
  +#include <limits>
  #include <map>
  #include <cmath>
  @@ -61,7 +62,7 @@ public:
  int circlePoints {100};
  RuntimePolicy policy {RuntimePolicy::seq};
  - double distThreshold {1e100};
  + double distThreshold {std::numeric_limits<double>::max()};
  private:
  bool m_verboseOutput {false};
  @@ -112,6 +113,7 @@ public:
  ->capture_default_str();
  app.add_option("-d,--dist-threshold", distThreshold)
  + ->check(axom::CLI::NonNegativeNumber)
  ->description("Distance threshold to search")
  ->capture_default_str();
  