message: tests: Add more XPath sorting tests
  Cover empty node case - no XPath query can result in that but it's
  possible to create a node set with empty nodes manually.
diff: @@ -672,6 +672,17 @@ TEST(xpath_sort_crossdoc_different_depth)
  CHECK((ns[0] == ns1[0] && ns[1] == ns2[0]) || (ns[0] == ns2[0] && ns[1] == ns1[0]));
  }
  +TEST_XML(xpath_sort_empty_node, "<node><child1/><child2/></node>")
  +{
  + xml_node n = doc.child(STR("node"));
  + xpath_node nodes[] = { n.child(STR("child2")), xml_node(), n.child(STR("child1")), xml_node() };
  + xpath_node_set ns(nodes, nodes + sizeof(nodes) / sizeof(nodes[0]));
  +
  + ns.sort();
  +
  + CHECK(!ns[0] && !ns[1] && ns[2] == nodes[2] && ns[3] == nodes[0]);
  +}
  +
  TEST(xpath_allocate_string_out_of_memory)
  {
  std::basic_string<char_t> query;
  