NotificationEvent: Fix missing review comment

Problem: Review comment for new or deleted file has been missed.

Solution: Just leave the comment without code if it is for a new or
deleted file.

app/models/NotificationEvent.java

@@ -279,6 +279,8 @@ private static String buildCommentedCodeMessage(ReviewComment reviewComment, Lan
                     }
                 }
                 message.append("```\n");
+            } else {
+                message.append(reviewComment.getContents());
             }
 
             return message.toString();