message: difficulty: Fix caculate next target panic
diff: @@ -56,6 +56,9 @@ pub fn get_next_work_required(chain: &dyn ChainReader, epoch: &EpochInfo) -> Res
  let mut avg_time: u64 = 0;
  let mut avg_target = U256::zero();
  let mut latest_block_index = 0;
  + if blocks.len() <= 1 {
  + return Ok(difficult_to_target(current_header.difficulty));
  + }
  let block_n = blocks.len() - 1;
  while latest_block_index < block_n {
  let solve_time =
  