Refactor:naive_merge_with_images close useless images (#9296)

### What problem does this PR solve?

naive_merge_with_images close useless images

### Type of change

- [x] Refactoring

rag/nlp/__init__.py

                 if re.match(f"^{dels}$", sub_sec):
                     continue
                 add_chunk(sub_sec, image)
+        
+        for img in images:
+            if isinstance(img, Image.Image):
+                img.close()
 
     return cks, result_images