message: Disallow minting 0 coins, fix
  Closes:
  Approved by: sunmilee
diff: @@ -294,6 +294,8 @@ impl ClientProxy {
  let receiver = self.get_account_address_from_parameter(space_delim_strings[1])?;
  let num_coins = Self::convert_to_micro_libras(space_delim_strings[2])?;
  + ensure!(num_coins > 0, "Invalid number of coins to mint.");
  +
  match self.faucet_account {
  Some(_) => self.association_transaction_with_local_faucet_account(
  transaction_builder::encode_mint_script(&receiver, num_coins),
  