code: function readSingleAddress(conn, handleAddress){
  	readSingleWallet(conn, function(wallet_id){
  		conn.query("SELECT address FROM my_addresses WHERE wallet=?", [wallet_id], function(rows){
  			if (rows.length === 0)
  				throw Error("no addresses");
  			if (rows.length > 1)
  				throw Error("more than 1 address");
  			handleAddress(rows[0].address);
  		});
  	})
  }
docs: read single address, If amount of addresses is bigger than one, will throw an error
  @param {object} conn - database connection
  @param {function} handleAddress - callback