let hdr0 = decode_slice_header(&mut br, bd, 0, slice_offs.as_slice(), self.width, self.height)?;
validate!((hdr0.width != 0) && (hdr0.height != 0));
self.width = hdr0.width;
let hdr0 = decode_slice_header(&mut br, bd, 0, slice_offs.as_slice(), self.width, self.height)?;
validate!((hdr0.width != 0) && (hdr0.height != 0));
self.width = hdr0.width;