QStyle::standardPixmap is deprecated and not hi-dpi friendly.
Unfortunately, there's no equivalent of QIcon::addPixmap
for QIcons themselves -- so it's **impossible** in current Qt
API to handle the ON/OFF icon states.
Believe me... there's NOOOOOOO way. I've looked. I've tried.
It's not possible.
This means we have to change the logic for showing open/closed
folders in browser. This commit revises the logic to show the
open icon for any *populated* folders, regardless of whether
they are opened or not.
