Fix the logic for Maximize / Minimize
The old logic is good but the splitters don't hide
themselves if all children is hidden, so we need to
hide them again.
Test Plan: The terminals seems a bit "cut" after restoration (this actually hits me with anything that shows / hides a session. @hindenburg any hint to fix this behavior completely?
Reviewers: ngraham, hindenburg, Konsole
Subscribers: hindenburg, konsole-devel
Differential Revision: https://phabricator.kde.org/D21308