A witness who is subpoenaed to attend criminal proceedings, shall attend the proceedings and remain in attendance at the proceedings, and a person who is in attendance at criminal proceedings, though not subpoenaed as a witness, and who is warned by the court to remain in attendance at the proceedings, shall remain in attendance at the proceedings, unless such witness or such person is excused by the court: Provided that the court may, at any time during the proceedings in question, order that any person, other than the accused, who is to be called as a witness, shall leave the court and remain absent from the proceedings until he is called, and that he shall remain in court after he has given evidence.