[2.3] Broken filter url builder

[dmolineus]

Checklist before I submit this issue report

I confirm that:

• [x] I have tested this with the latest version available
• [x] I have read documentation @ http://metamodels.readthedocs.org/en/ or http://metamodels.readthedocs.org/de/
• [x] I have checked the Contao community forums for references https://community.contao.org/
• [x] I have checked existing issues for duplicates and found none @ https://github.com/MetaModels/core/issues?q=is%3Aissue

My environment is:

(Please fill in the actual values from your environment - check Contao Manager or use composer show)

Key	Value	Comments
PHP version:	8.1.16
Contao version:	4.13.16
MetaModels version:	2.3@dev
Installed MetaModels packages:
DCG version:	2.3@dev

Issue description

When using the new routing MetaModels breaks even though #1492 is marked as closed.

Steps to reproduce

1. Given a MetaModels list
2. The FilterUrlBuilder tries to retrieve the route information from the current request. In the list controller the _route attribute is not set. The main request has to be used
3. Given a fragment foo/bar the filter url build tries to set a slug bar=null. This breaks because a string value is required

Describe the behaviour of the application

UnkownRouteNameException or type error is thrown.

[zonky2]

Fixed in MM 2.3

Note: On the 40*-pages, an MM list can be output but no URLs can be created, e.g. for pagination, filtering or sorting - Contao prevents routing to this page type.