It’s a question that haunts any marriage, especially once anniversaries start to become marked not in years, but in decades. Is there still a spark? When it comes to the revival of the ’90s sitcom Mad About You, launching Wednesday on Spectrum cable’s on-demand platform 20 years after the original series finale, it is the question. But, you see, Helen Hunt and Paul Reiser like each other. A lot. It’s why their marriage works.