fix(context): log warning when platform not found for session

Author: Soulter

astrbot/core/star/context.py

@@ -457,6 +457,7 @@ async def send_message(
             if platform.meta().id == session.platform_name:
                 await platform.send_by_session(session, message_chain)
                 return True
+        logger.warning(f"cannot find platform for session {session.platform_name}, message not sent")
         return False
 
     def add_llm_tools(self, *tools: FunctionTool) -> None: