Where an accused person has, on conviction, been sentenced to imprisonment for a term, not being imprisonment in default of payment of fine, the period of detention, if any, undergone by him during the investigation, inquiry or trial of the same case and before the date of such conviction, shall be set off against the term of imprisonment imposed on him on such conviction, and the liability of such person to undergo imprisonment on such conviction shall be restricted to the remainder, if any, of the term of imprisonment imposed on him:

   Provided that in cases referred to in section 475, such period of detention shall be set off against the period of fourteen years referred to in that section.