Remove unwrap and return an error in store/reader

[fulmicoton]

if alive {
                    let ret = Some((
                        curr_block.as_ref().unwrap().as_ref().unwrap().clone(), // todo forward errors
                        num_skipped,
                        reset_block_pos,
                    ));
                    // the map block will move over the num_skipped, so we reset to 0
                    num_skipped = 0;
                    ret
                } else {
                    None
                }

Remove unwrap here.