fix(kb): skip knowledge base retrieval if query is empty or whitespace

Author: Rat0323

astrbot/core/knowledge_base/retrieval/manager.py

@@ -87,6 +87,9 @@ async def retrieve(
             List[RetrievalResult]: 检索结果列表
 
         """
+        if not isinstance(query, str) or not query.strip():
+            return []
+
         if not kb_ids:
             return []