From left to right: Celeste Den (Jean) and Shannon Cochran (Harriet) in "POTUS" at Geffen Playhouse (Photo by Jeff Lorch). About an hour before curtain at the Geffen Playhouse last Friday night, Vice President Kamala Harris was purported to be dining around the corner in Westwood, escorted by a police motorcade flashing red and blue to a restaurant on Glendon Ave. barricaded by large SUVs.   Coincidence? Though the vice president was not immediately visible at the Geffen Play