guard against null root.value in Marquee (???)

ui/src/components/Marquee.vue

@@ -20,7 +20,7 @@ export default defineComponent({
     speed: {
       default: 30,
       type: Number,
-    }
+    },
   },
   setup(props) {
     const root = ref<HTMLDivElement | null>(null);
@@ -31,6 +31,7 @@ export default defineComponent({
 
     onMounted(() => {
       const resizeObserver = new ResizeObserver(() => {
+        if (!root.value) return;
         overflowed.value = root.value!.scrollWidth > root.value!.clientWidth;
         shiftWidth.value = `-${
           inner.value!.clientWidth - root.value!.clientWidth