sent invite check pre username if exists

resources/lang/en/user.php

@@ -54,4 +54,5 @@ return [
             'body' => 'You had been :action to :new_class, administrator: :operator, reason: :reason.',
         ],
     ],
+    'username_already_exists' => 'Username::username already exists',
 ];

resources/lang/zh_CN/user.php

@@ -54,4 +54,5 @@ return [
             'body' => '你被:action为:new_class，管理员：:operator, 原因：:reason。',
         ],
     ],
+    'username_already_exists' => '用户名：:username 已经存在',
 ];

resources/lang/zh_TW/user.php

@@ -54,4 +54,5 @@ return [
             'body' => '你被:action為:new_class，管理員：:operator, 原因：:reason。',
         ],
     ],
+    'username_already_exists' => '用戶名：:username 已經存在',
 ];