Grammar check fixed

@@ -618,7 +618,7 @@ function handleEvent(event) {
                                 if (detect_body.langCode = 'en') {
                                     var grammar = {
                                         url: EnGrammarCheck_api_url,
-                                        form: {key: '9WUGcY6ZayYMphG7', text: event.message.text},
+                                        form: {key: config.textgear_config.key, text: event.message.text},
                                     }
                                     request.post(grammar, function (error, response, body) {
                                         if (!error && response.statusCode == 200) {
@@ -640,8 +640,10 @@ function handleEvent(event) {
                                             result.text = temp;
 
                                             var last_index = Object.keys(objBody.errors).length -1;
-                                            result.text += event.message.text.substring(objBody.errors[last_index]['offset'] + objBody.errors[last_index]['length'], event.message.text.length);
 
+                                            if(last_index >=0) {
+                                                result.text += event.message.text.substring(objBody.errors[last_index]['offset'] + objBody.errors[last_index]['length'], event.message.text.length);
+                                            }
                                             //번역된 문장 보내기
                                             client
                                                 .replyMessage(event.replyToken, result)
@@ -704,4 +706,4 @@ function handleEvent(event) {
 
 app.listen(3000, function () {
     console.log("Linebot listening on port 3000!");
-});
\ No newline at end of file
+});