128. Privilege not waived by volunteering evidence.- If any party to a suit gives evidence therein at his own instance or otherwise, he shall not be deemed to have consented thereby to such disclosure as is mentioned in section 126; and if any party to a suit or proceeding calls any such barrister, 1[ pleader], attorney or vakil as a witness, he shall be deemed to have consented to such disclosure only if he questions such barrister, attorney or vakil on matters which, but for such question, he would not be at liberty to disclose.