message: demo: Fix normal component signs in PackedVertex
  We're encoding signed normal components or signed octahedral encoding
  results, so the type should be signed.
diff: @@ -297,7 +297,7 @@ struct PackedVertex
  {
  unsigned short px, py, pz;
  unsigned short pw; // padding to 4b boundary
  - unsigned char nx, ny, nz, nw;
  + signed char nx, ny, nz, nw;
  unsigned short tx, ty;
  };
  @@ -326,7 +326,7 @@ void packMesh(std::vector<PackedVertex>& pv, const std::vector<Vertex>& vertices
  struct PackedVertexOct
  {
  unsigned short px, py, pz;
  - unsigned char nu, nv; // octahedron encoded normal, aliases .pw
  + signed char nu, nv; // octahedron encoded normal, aliases .pw
  unsigned short tx, ty;
  };
  