message: Add current head predecessor into missing blocks
  Before this change we relied only on history field, but history field can be empty at times.
diff: @@ -198,6 +198,9 @@ impl ChainManager {
  match message {
  PeerMessage::CurrentBranch(message) => {
  debug!(log, "Received current branch");
  + if message.current_branch().current_head().level() > 0 {
  + block_state.push_missing_block(message.current_branch().current_head().predecessor().clone().into())?;
  + }
  message.current_branch().history().iter().cloned().rev()
  .map(|history_block_hash| block_state.push_missing_block(history_block_hash.into()))
  .collect::<Result<Vec<_>, _>>()?;
  