libtaskmanager: Fix filter by virtual desktop when screens change

Original commit message(s)

• libtaskmanager: Fix filter by virtual desktop when screens change

Now that we have virtual desktops per output, we need to invalidate the filter when the screen geometry changes.

Furthermore, when all outputs are removed, the window's reported screen geometry can be empty which will skip the filter, so we need to re-trigger it again when the window's screen geometry comes back.

Reason for the change

Since KWin removes all outputs when switching to TTY, I found that when coming back, all windows would be shown until some change (opening new window, window changing title, etc) caused it to update.

Test plan

Have multiple virtual desktops (multiple screens are not required, I reproduced it on my laptop), switch to TTY, switch back.