:recycle: checking for intersection observer before clearing on load

vue-theme/src/pages/list.vue

@@ -179,7 +179,7 @@ export default {
         },
         unsetIntersectionLoader() {
             const footerEl = document.querySelector(INTERSECT_SELECTOR)
-            if(!footerEl) return
+            if(!footerEl || !this.observer) return
 
             console.warn('unsetting intersection handler on:', footerEl, this.sortBy)
             this.observer.unobserve(footerEl)