Prevent focusing next task if focused task part of split select

* Also ensure that in tablet portrait we shift
thumbnails to prevent overlap with the placeholder
view. I'm guessing the time that was written maybe
the grid was taking up a smaller space?

Fixes: 199898622
Test: Go into split selection with focused task,
next task doesn't take focus. Grid shifts down
to not overlap with placeholder view.

Change-Id: I4ed37b1d28287685ad01885331dffd764c7ddfc9