TAIPEI — A Chinese war plane goes missing near Taiwan. China sends swarms of military boats and planes for a blockade as Taiwan goes on a war footing. Panic ensues on the streets of Taipei. The premise of “Zero Day,” a new Taiwan TV drama envisioning a Chinese invasion, is a topic that has for years been considered too sensitive for many Taiwan filmmakers and television show creators, who fear losing access to the lucrative Chinese entertainment market. But as China steps up military threats, including the large massing of naval forces last week and daily military activities close to