Add checks for container presence in animation functions to prevent errors when elements are removed from the DOM [skip ci]

Jellyfin.Plugin.Seasonals/Web/fireworks.js

@@ -162,6 +162,7 @@ function startFireworks() {
   }
 
   fireworksInterval = setInterval(() => {
+    if (!document.body.contains(fireworkContainer)) { clearInterval(fireworksInterval); return; }
     const randomCount = Math.floor(Math.random() * maxFireworks) + minFireworks;
     for (let i = 0; i < randomCount; i++) {
       setTimeout(() => {