`neos/content` throws 500 if no site exists and menu drawer is not accessible

[mhsdesign]

There will be a sitedetection failed exception in the neos/content route when the backend controller cannot find a site.

In 8.3 we dont have a graceful error as well only something like Site doest not exist for current user: https://github.com/neos/neos-ui/issues/3182

We should probably redirect to some other available module, or at least keep the backend frame around and not destroy everything.

Originally posted by @mhsdesign in https://github.com/neos/neos-development-collection/pull/4717#discussion_r1492609325