Pre-existing redirect in different node dimension are overriden

[neos-bot]

Jira issue originally created by user @gerhard-boden:

Testcase:
We have an existing redirect like: someoldsite.html that points to de/newcontent in the german content dimension.

When activating a previously hidden document /en/newcontentin the english dimension the following redirects are generated:
de/newcontent => en/newcontent (unwanted, but does at least not do anything since the german page exists)

AND

someoldsite.html => en/newcontent. The former redirect to de/newcontent deleted.

Jira-URL: https://jira.neos.io/browse/NEOS-1869