When setting-up the plasma window interface we need to call
`setOnAllDesktops()` after the actual virtual desktops have
been set.

Otherwise, the current desktop would be always added to the
interface (as if the user were unsetting the "onAllDesktops"
flag) and the plasma interface and KWin can get un-synced,
specially if there are specific window rules.

BUG: 452171
FIXED-IN: 5.24.5


(cherry picked from commit 4c8711f1)