allow username to be set by admin, when username is empty

src/js/client.js

@@ -1819,6 +1819,7 @@ angular.module('Application').service('Client', ['$http', '$interval', '$timeout
             active: user.active,
             role: user.role
         };
+        if (user.username) data.username = user.username;
 
         post('/api/v1/users/' + user.id, data, null, function (error, data, status) {
             if (error) return callback(error);