chore: [lazy canvas rendering] check whether observer exist before disconnecting while cleaning up (#21171)

Fixes #20558

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app/client/src/widgets/withLazyRender.tsx

@@ -55,7 +55,7 @@ export function withLazyRender(Widget: typeof BaseWidget) {
 
       return () => {
         (window as any).cancelIdleCallback(idleCallbackId);
-        observer.disconnect();
+        observer && observer.disconnect();
       };
     }, []);