Default initialize node's member variable (jbeder#923)

Author: k0zmo

include/yaml-cpp/node/detail/node.h

@@ -24,7 +24,7 @@ class node {
   };
 
  public:
-  node() : m_pRef(new node_ref), m_dependencies{} {}
+  node() : m_pRef(new node_ref), m_dependencies{}, m_index{} {}
   node(const node&) = delete;
   node& operator=(const node&) = delete;