fix(exam/bodypositionlist): use default thumbnail when position image fails to load

src/pages/exam/components/ImageViewer.tsx

@@ -1,5 +1,6 @@
 import React from 'react';
 import { Image } from 'antd';
+import defaultPosition from 'src/assets/imgs/default-position.png';
 
 interface ImageViewerProps {
   src: string;
@@ -16,7 +17,13 @@ const ImageViewer: React.FC<ImageViewerProps> = ({
 }) => {
   return (
     <div className={`image-viewer ${className}`}>
-      <Image src={src} alt={alt} onClick={onClick} preview={false} />
+      <Image
+        src={src}
+        alt={alt}
+        onClick={onClick}
+        preview={false}
+        fallback={defaultPosition}
+      />
     </div>
   );
 };