Create application directory if it doesn't exist

Unlike KStandardDirs, QStandardDirs doesn't guarantee that the returned
directory actually exists, see also
https://community.kde.org/Frameworks/Porting_Notes/KStandardDirs .

This patch checks for the existence of the directory and creates it if
it isn't there, before the game state is saved.

BUG: 350160
FIXED-IN: 15.08.2
REVIEW: 125508