Fix: Correct positioning logic for bottom action toolbar

Currently, the bottom toolbar uses screen height instead of viewport bounds, causing it to clip on some setups. I think this is especially an issue with vertically ordered multi-monitor setups.

This fix changes the logic to check against viewportRect.bottom, to force the bottom toolbar to appear over the screenshot instead of below of the screen (probably only happening on multi monitor setups).

Behavior before (Toolbar is clipped off):

Behavior now (Toolbar is still visible and appears on top of the screenshot):

This is my first commit to KDE, so I am happy for any feedback or recommendations!

Greetings