message: Small adjustment to apng documentation
diff: @@ -174,8 +174,10 @@ impl<R: Read> PngDecoder<R> {
  /// Returns if the image contains an animation.
  ///
  - /// Note that file decides if the default image is considered to be part of the animation. When
  - /// it is not the common interpretation is to use it as a thumbnail.
  + /// Note that the file itself decides if the default image is considered to be part of the
  + /// animation. When it is not the common interpretation is to use it as a thumbnail.
  + ///
  + /// If a non-animated image is converted into an `ApngDecoder` then its iterator is empty.
  pub fn is_apng(&self) -> bool {
  self.reader.info().animation_control.is_some()
  }
  