No bank or trust company shall purchase shares of its own capital stock, nor make any loan on the faith or pledge of shares of its own capital stock; but nothing in this section shall inhibit such purchase or loan when necessary to prevent loss on debts created prior to March 31, 1921, nor shall it affect the holding of stock acquired by any bank or trust company prior to March 31, 1921. Notwithstanding the foregoing, the Commissioner may approve the purchase by a bank or trust company of the shares of its own capital stock, subject to such terms and conditions, if any, as the Commissioner may require.