I don’t normally steer readers in the direction of this show, but tonight’s Lip Sync Battle features a duel that’s truly worth checking out, if only because it seems too entirely improbable. The battle is between two former network late-night talk-show hosts, Jay Leno and Craig Ferguson, both of whom have a little more time on their hands than they used to. But the musical selections performed in competition here are both telling and jarring: Leno, for example, dons a leather jacket to swagger his way through Sweet’s “Ballroom Blitz.”