fix: ensure title_aided_config is defined before accessing its properties

mineru/backend/vlm/token_to_middle_json.py

@@ -12,8 +12,9 @@ from mineru.version import __version__
 
 heading_level_import_success = False
 llm_aided_config = get_llm_aided_config()
-title_aided_config = llm_aided_config.get('title_aided', {})
-if llm_aided_config and title_aided_config.get('enable', False):
+if llm_aided_config:
+    title_aided_config = llm_aided_config.get('title_aided', {})
+    if title_aided_config.get('enable', False):
         try:
             from mineru.utils.llm_aided import llm_aided_title
             from mineru.backend.pipeline.model_init import AtomModelSingleton