Add testcases for Username

Author: arifszn

tests/Rules/UsernameTest.php

@@ -44,6 +44,8 @@ public function provider()
             [false, 'ｆｏｏbar'],
             [false, '😀'],
             [false, 'john😀'],
+            [false, ''],
+            [false, '  '],
         ];
     }
 }