fix(lazyloader): fix trying to run inexistent callbacks (#833)

packages/scenes/src/components/layout/LazyLoader.tsx

@@ -52,8 +52,8 @@ export const LazyLoader: LazyLoaderType = React.forwardRef<HTMLDivElement, Props
       }
 
       return () => {
-        delete LazyLoader.callbacks[id];
         wrapperEl && LazyLoader.observer.unobserve(wrapperEl);
+        delete LazyLoader.callbacks[id];
         if (Object.keys(LazyLoader.callbacks).length === 0) {
           LazyLoader.observer.disconnect();
         }
@@ -62,8 +62,8 @@ export const LazyLoader: LazyLoaderType = React.forwardRef<HTMLDivElement, Props
 
     // If the element was loaded, we add the `hideEmpty` class to potentially
     // hide the LazyLoader if it does not have any children. This is the case
-    // when children have the `isHidden` property set. 
-    // We always include the `className` class, as this is coming from the 
+    // when children have the `isHidden` property set.
+    // We always include the `className` class, as this is coming from the
     // caller of the `LazyLoader` component.
     const classes = `${loaded ? hideEmpty : ''} ${className}`;
     return (
@@ -90,7 +90,9 @@ LazyLoader.addCallback = (id: string, c: (e: IntersectionObserverEntry) => void)
 LazyLoader.observer = new IntersectionObserver(
   (entries) => {
     for (const entry of entries) {
-      LazyLoader.callbacks[entry.target.id](entry);
+      if (typeof LazyLoader.callbacks[entry.target.id] === 'function') {
+        LazyLoader.callbacks[entry.target.id](entry);
+      }
     }
   },
   { rootMargin: '100px' }