fix: Breakage of message pane when Openai integration isn't enabled (#8381)

Error when the Openai integration isn't enabled

fixes: https://github.com/chatwoot/chatwoot/issues/8379

app/javascript/dashboard/mixins/aiMixin.js

@@ -18,7 +18,7 @@ export default {
     aiIntegration() {
       return this.appIntegrations.find(
         integration => integration.id === 'openai' && !!integration.hooks.length
-      ).hooks[0];
+      )?.hooks[0];
     },
     isAIIntegrationEnabled() {
       return !!this.aiIntegration;