优化查询条件，适合复合索引

app/Http/Controllers/Api/MessageController.php

@@ -15,7 +15,7 @@ class MessageController extends Controller
 {
     public function index()
 	{
-		$list = Message::where('user_id', $this->user_id)
+		$list = Message::where(['agent_id' => $this->agent_id, 'user_id' => $this->user_id])
 			->select('id', 'title', 'is_read', 'created_at')
 			->orderBy('id', 'DESC')
 			->simplePaginate(15);