Open redirect through HTML conversion request filter

Steps to reproduce:

Open <xwiki-host>/xwiki/bin/view/Main/?foo=bar&foo_syntax=invalid&RequiresHTMLConversion=foo&xerror=https://www.example.com where <xwiki-host> is the URL of your XWiki installation.

Expected result:

No redirect is performed, an error is possibly displayed.

Actual result:

The browser is redirected to https://www.example.com. This demonstrates an open redirect vulnerability that could be used, e.g., for phishing attacks.

This has been reported on SonarCloud, see https://sonarcloud.io/project/issues?open=AXnpAhzJDDFOvAKXAQy3&id=org.xwiki.platform%3Axwiki-platform.