The owner, licensee, or operator of a visual or sound radio broadcasting station, or network of stations, or agents or employees of any such owner, licensee, or operator shall not be liable for any damages for any defamatory statement published or uttered in or as a part of any visual or sound radio broadcast by or on behalf of any candidate for public office; Provided, however, that this exemption from liability shall not apply to any owner, licensee, or operator, or agent or employee of any owner, licensee, or operator of such visual or sound radio broadcasting station, or network of stations, when such owner, licensee, or operator, or agent or employee of the owner, licensee, or operator of such visual or sound radio broadcasting station is a candidate for public office or speaking on behalf of a candidate for public office.