message: Return -1 for error in printf
diff: @@ -97,11 +97,11 @@ pub unsafe fn printf<W: Write>(mut w: W, format: *const c_char, mut ap: VaList)
  '#' => Ok(()),
  '0'...'9' => Ok(()),
  _ => Ok(()),
  - }.expect("Error writing!")
  + }.map_err(|_| return -1).unwrap()
  } else if b == b'%' {
  found_percent = true;
  } else {
  - w.write_u8(b).expect("Error writing char!");
  + w.write_u8(b).map_err(|_| return -1).unwrap()
  }
  }
  