On a whim, I went to see Margaret Cho’s new concert film, “Notorious C.H.O.” on Wednesday evening. It’s frequently hilarious and I admire the nose-to-the-grindstone way she has rebuilt her post-“All-American Girl” career. I didn’t realize until arriving at the theater that it was opening night, or that Cho would be there in person, or that she was going to be actually standing at the theater door, greeting moviegoers and taking each person’s ticket. It was a cute gesture.