fix(chat): 修复计划过滤器和消息构建器中的潜在空指针问题

- 在 `plan_filter.py` 中，当LLM未指定 `target_message_id` 时，明确将目标消息设置为最新的消息，避免后续操作因 `target_message_dict` 未定义而出错。
- 在 `chat_message_builder.py` 中，为 `replace_user_references_sync` 函数增加了对 `content` 为空的检查，防止后续处理引发异常。
- 将数据库查询从 `.scalar()` 改为 `.scalar_one_or_none()`，以更清晰地处理未找到结果的情况。

src/chat/planner_actions/plan_filter.py

@@ -233,8 +233,10 @@ class PlanFilter:
             if action not in ["no_action", "no_reply", "do_nothing", "proactive_reply"]:
                 if target_message_id := action_json.get("target_message_id"):
                     target_message_dict = self._find_message_by_id(target_message_id, message_id_list)
-                    if target_message_dict is None:
+                else:
+                    # 如果LLM没有指定target_message_id，我们就默认选择最新的一条消息
                     target_message_dict = self._get_latest_message(message_id_list)
+
                 if target_message_dict:
                     from src.common.data_models.database_data_model import DatabaseMessages
                     target_message_obj = DatabaseMessages(**target_message_dict)

src/chat/utils/chat_message_builder.py

@@ -35,6 +35,9 @@ def replace_user_references_sync(
     Returns:
         str: 处理后的内容字符串
     """
+    if not content:
+        return ""
+        
     if name_resolver is None:
         person_info_manager = get_person_info_manager()
 
@@ -817,8 +820,8 @@ def build_pic_mapping_info(pic_id_mapping: Dict[str, str]) -> str:
         description = "[图片内容未知]"  # 默认描述
         try:
             with get_db_session() as session:
-                image = session.execute(select(Images).where(Images.image_id == pic_id)).scalar()
+                image = session.execute(select(Images).where(Images.image_id == pic_id)).scalar_one_or_none()
-                if image and image.description:
+                if image and image.description: # type: ignore
                     description = image.description
         except Exception:
             # 如果查询失败，保持默认描述