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:
(a) where the holder in good faith and by mistake inserts a wrong date; and
(b) 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.