Jay and Mavis Leno were spotted walking hand-in-hand after catching a comedy show in Los Angeles earlier this week. The famed late-night talk show host, 74, has been lovingly caring for his wife, 78, since she was diagnosed with advanced Alzheimer’s disease. He is often seen attending events with her or driving her around town as they run errands together. Jay was photographed holding Mavis’ hand while sporting a dark blue suit and white shirt. The 78-year-old wore a long-sleeved, floral-print top, black pants and light blue sneakers. As OK! previously reported, Jay was approved to be his wife…