make sure no newlines exist in buffer

rplugin/python3/handlers/chat_handler.py

@@ -227,7 +227,7 @@ def _add_chat_messages(
             token = buffer[: last_newline]
 
             # Remove the token and newline from the buffer
-            buffer = buffer[last_newline + 1:]
+            buffer = buffer.replace(token, "").replace("\n", "")
 
             self.nvim.exec_lua(
                 'require("CopilotChat.utils").log_info(...)', f"Token: {token}"