fix: movewindoworgroup onto empy workspace on next monitor

[muellerbernd]

Describe your PR, what does it fix/add?

I had the problem when using movewindoworgroup, that if I want to move the current window(that is not inside a group) onto an empty workspace on another monitor, the movewindoworgroup did not behave like movewindow and I was not able to move the window. With movewindow everything worked fine.

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

I tested the code on my NixOS machine and it worked like I expected. Please let me know if there is an easier fix for that.