WASHINGTON — Caleb Thielbar still can channel humor amid a challenging stretch for the Chicago Cubs’ 39-year-old lefty reliever. He entered the Cubs’ three-game series against the Washington Nationals without walking a batter in his last 15 appearances, avoiding a free pass since June 29. “Oh great, we can’t talk about that,” Thielbar said wryly before Tuesday’s series opener. The lack of ...