Login screen: entering the wrong password breaks the redirect

[ogoffart]

This bug was initially reported in owncloud/oauth2#47 , but it's actually valid for every redirection.

Steps to reproduce

1. Make sure that you are logged out of owncloud.
2. Go to some specific URL, such as https://<server_url>/index.php/settings/personal?section=apppasswords
3. On the login page, enter the wrong password. (can happen, everybody makes mistakes ☺) Observe that the redirect_url parameter in the URL disapear
4. On the second attempt, use the right password
5. Get redirected to the homepage instead of the page you were trying to reach

Expected behaviour

After login, we should be redirected to the page we're trying to reach, even after a failed attempt.

Actual behaviour

If we make a failed attempt, we go to the home instead.

Server configuration

ownCloud version: Tested with ownCloud 9.1.3 (stable) and master branch.