message: vertexcodec: Store vertex block size before each block
  This allows us to split blocks arbitrarily if we need to, and makes
  index prediction loop simpler since we don't need to slice vertices into
  groups of precisely 256 elements.
diff: @@ -15,7 +15,9 @@ static unsigned char* encodeVertexBlock(unsigned char* data, const unsigned char
  {
  (void)prediction;
  - assert(vertex_count > 0);
  + assert(vertex_count > 0 && vertex_count <= 256);
  +
  + *data++ = static_cast<unsigned char>(vertex_count - 1);
  for (size_t k = 0; k < vertex_size; ++k)
  {
  