refactor(app): 优化邮件模板

app/Console/Commands/UpdateLetter.php

@@ -43,7 +43,10 @@ class UpdateLetter extends Command
     public function handle()
     {
         // 更新用户首字母
-        $users = User::whereNull('letter')->whereNotNull('name')->limit(100)->get();
+        $users = User::whereNull('letter')
+            ->where(function ($query) {
+                $query->whereNotNull('name')->orWhereNotNull('username');
+            })->limit(100)->get();
         foreach ($users as $user) {
             $name = $user->username;
             if ($user->name) {