feat(Message): prevent fetching an interaction webhook. (#6468)

src/errors/Messages.js

@@ -103,6 +103,7 @@ const Messages = {
   WEBHOOK_MESSAGE: 'The message was not sent by a webhook.',
   WEBHOOK_TOKEN_UNAVAILABLE: 'This action requires a webhook token, but none is available.',
   WEBHOOK_URL_INVALID: 'The provided webhook URL is not valid.',
+  WEBHOOK_APPLICATION: 'This message webhook belongs to an application and cannot be fetched.',
   MESSAGE_REFERENCE_MISSING: 'The message does not reference another message',
 
   EMOJI_TYPE: 'Emoji must be a string or GuildEmoji/ReactionEmoji',

src/structures/Message.js

@@ -788,6 +788,7 @@ class Message extends Base {
    */
   fetchWebhook() {
     if (!this.webhookId) return Promise.reject(new Error('WEBHOOK_MESSAGE'));
+    if (this.webhookId === this.applicationId) return Promise.reject(new Error('WEBHOOK_APPLICATION'));
     return this.client.fetchWebhook(this.webhookId);
   }