PLT-7521: improve regex pattern (#7345)

* PLT-7521: improve regex pattern

* style fix

webapp/components/login/login_controller.jsx

@@ -210,7 +210,7 @@ export default class LoginController extends React.Component {
     finishSignin(team) {
         const query = this.props.location.query;
         GlobalActions.loadCurrentLocale();
-        if (query.redirect_to && query.redirect_to.match(/^\//)) {
+        if (query.redirect_to && query.redirect_to.match(/^\/([^/]|$)/)) {
             browserHistory.push(query.redirect_to);
         } else if (team) {
             browserHistory.push(`/${team.name}`);