I wonder if it could be a deleted scene that was shown at a convention years after the fact, and THAT is what the OP is remembering? I have both the broadcast and theatrical versions on DVD, and neither have it.
Right after I first frond this thread, I went looking for my copy of the novelization, hoping to find the scene there, but now, I can't find the book. The only thing I DID discover is that my bookcases are not filed the way I thought they were.
Nope, never been to a convention in my life. It was broadcast in 1979 and that scene stuck with me.