Evidence of a statement previously made by a witness that is consistent with his testimony at the hearing is inadmissible to support his credibility unless it is offered after:
(a) Evidence of a statement made by him that is inconsistent with any part of his testimony at the hearing has been admitted for the purpose of attacking his credibility, and the statement was made before the alleged inconsistent statement; or
(b) An express or implied charge has been made that his testimony at the hearing is recently fabricated or is influenced by bias or other improper motive, and the statement was made before the bias, motive for fabrication, or other improper motive is alleged to have arisen.