message: Stop generating empty `Mesh2D` in `canvas::Frame`
diff: @@ -262,6 +262,7 @@ impl Frame {
  ///
  /// [`Frame`]: struct.Frame.html
  pub fn into_primitive(mut self) -> Primitive {
  + if !self.buffers.indices.is_empty() {
  self.primitives.push(Primitive::Mesh2D {
  origin: Point::ORIGIN,
  buffers: triangle::Mesh2D {
  @@ -269,6 +270,7 @@ impl Frame {
  indices: self.buffers.indices,
  },
  });
  + }
  Primitive::Group {
  primitives: self.primitives,
  