message: Use read_into_buffer, which deinterlaces as needed
diff: @@ -181,7 +181,7 @@ impl<R: Read> Iterator for GifFrameIterator<R> {
  }
  let mut vec = vec![0; self.reader.buffer_size()];
  - if let Err(err) = self.reader.fill_buffer(&mut vec) {
  + if let Err(err) = self.reader.read_into_buffer(&mut vec) {
  return Some(Err(err.into()));
  }
  