message: demo: Extend indexcodec coverage test
  Our current test doesn't use data section, which means we aren't
  triggering some out-of-bounds checks; we now have a triangle that we
  can't encode efficiently in the mix.
diff: @@ -536,9 +536,9 @@ void encodeIndex(const Mesh& mesh)
  void encodeIndexCoverage()
  {
  - const unsigned int indices[] = { 0, 1, 2, 2, 1, 3 };
  + const unsigned int indices[] = { 0, 1, 2, 2, 1, 3, 4, 6, 5 };
  const size_t index_count = sizeof(indices) / sizeof(indices[0]);
  - const size_t vertex_count = 4;
  + const size_t vertex_count = 7;
  std::vector<unsigned char> buffer(meshopt_encodeIndexBufferBound(index_count, vertex_count));
  buffer.resize(meshopt_encodeIndexBuffer(&buffer[0], buffer.size(), indices, index_count));
  