message: utils: fix overflow within round_up_4k()
  Input size 0 should be rounded up to 0. But now it is a
  illegal value casuing overflow panic.
diff: @@ -29,6 +29,9 @@ pub fn div_round_up(n: u64, d: u64) -> u64 {
  }
  pub fn round_up_4k(x: u64) -> Option<u64> {
  + if x == 0 {
  + return Some(0);
  + }
  ((x - 1) | 4095u64).checked_add(1)
  }
  @@ -88,6 +91,7 @@ mod tests {
  #[test]
  fn test_rounders() {
  + assert_eq!(round_down_4k(0), 0);
  assert_eq!(round_down_4k(100), 0);
  assert_eq!(round_down_4k(4300), 4096);
  assert_eq!(round_down_4k(4096), 4096);
  @@ -95,7 +99,8 @@ mod tests {
  assert_eq!(round_down_4k(4097), 4096);
  assert_eq!(round_down_4k(u64::MAX - 1), u64::MAX - 4095);
  assert_eq!(round_down_4k(u64::MAX - 4095), u64::MAX - 4095);
  - assert_eq!(round_down_4k(0), 0);
  + assert_eq!(round_up_4k(0), Some(0));
  + assert_eq!(round_up_4k(1), Some(4096));
  assert_eq!(round_up_4k(100), Some(4096));
  assert_eq!(round_up_4k(4100), Some(8192));
  assert_eq!(round_up_4k(4096), Some(4096));
  