message: vertexcodec: Fix zigzag8 on systems with -funsigned-char
  zigzag8 needs to do an arithmetic shift right on an 8-bit value; we were
  previously assuming that char is signed, but on some systems it's
  unsigned. Meshes encoded on systems like this wouldn't be decodable.
diff: @@ -50,7 +50,7 @@ static size_t getVertexBlockSize(size_t vertex_size)
  inline unsigned char zigzag8(unsigned char v)
  {
  - return (char(v) >> 7) ^ (v << 1);
  + return ((signed char)(v) >> 7) ^ (v << 1);
  }
  inline unsigned char unzigzag8(unsigned char v)
  