refactor(db): 优化ChromaDB查询参数处理

将查询参数动态构建，仅在`where`条件存在时才将其添加到查询中。此举增强了代码的健壮性和灵活性，避免了传入空的`where`字典可能引发的潜在问题。

src/common/vector_db/chromadb_impl.py

@@ -92,12 +92,14 @@ class ChromaDBImpl(VectorDBBase):
         collection = self.get_or_create_collection(collection_name)
         if collection:
             try:
-                return collection.query(
-                    query_embeddings=query_embeddings,
-                    n_results=n_results,
-                    where=where or {},
+                query_params = {
+                    "query_embeddings": query_embeddings,
+                    "n_results": n_results,
                     **kwargs,
-                )
+                }
+                if where:
+                    query_params["where"] = where
+                return collection.query(**query_params)
             except Exception as e:
                 logger.error(f"查询集合 '{collection_name}' 失败: {e}")
         return {}