fix override custom error message

Author: HenryHengZJ

dist/web.js

@@ -376,7 +376,7 @@ export const Bot = (botProps: BotProps & { class?: string }) => {
   const updateErrorMessage = (errorMessage: string) => {
     setMessages((prevMessages) => {
       const allMessages = [...cloneDeep(prevMessages)];
-      allMessages.push({ message: errorMessage, type: 'apiMessage' });
+      allMessages.push({ message: props.errorMessage || errorMessage, type: 'apiMessage' });
       addChatMessage(allMessages);
       return allMessages;
     });