Arlington-based comic book editor Jason Rodriguez’s new graphic anthology, Postcards: True Stories that Never Happened, musters a cast of 33 cartoonists and lets them loose with the same premise: While accompanying his girlfriend on an antique-shopping trip, Rodriguez acquired a collection of decades-old postcards, the meanings of the cryptic, private messages scrawled on them long since lost to time. Rodriguez had each of his teams of creators choose one card and tell the story…