Pressing Clone shortcut when focused on cloned window creates new cloned window

[bartlomiejcieszkowski]

Steps to reproduce:

1. Open slides, eg. https://remarkjs.com/
2. Press c to clone slideshow.
3. Press c on cloned window it creates new cloned window. Furthermore changing slides on clone#1/clone#2 changes slides only on them, not on main window. Synchronization is only enabled between n and n-1 window.

Expected result:

Pressing C on cloned window won't create new window /or the cloned windows are dependant (eg. main window + n synchronized windows)

Issue is quite easy to reproduce accidentaly, since focus is changed to new cloned window. And pressing C twice in succession.

[tripu]

Well spotted, @bartlomiejcieszkowski :+1: