Where a bill expressed to be payable at a fixed period after date is issued undated, or where the acceptance of a bill payable at a fixed period after sight is undated, any holder may insert therein the true date of issue or acceptance, and the bill shall be payable accordingly. Provided that (1) where the holder in good faith and by mistake inserts a wrong date, and (2) in every case where a wrong date is inserted, if the bill subsequently comes into the hands of a holder in due course the bill shall not be avoided thereby, but shall operate and be payable as if the date so inserted had been the true date.