Fix KStandardDirs::locateLocal() porting

Summary:
KStandardDirs::locateLocal() created the directory if the requested
file and/or directory did not exist and returned the path. This
was not considered during porting to QStandardPaths

Test Plan:
- remove local palapeli config files (~/.local/share/palapeli/)
- start palapeli, shipped puzzles should appear and
  ~/.local/share/palapeli/collection/ should contain a '.puzzle'
  file for every puzzle.
-  Try to create a new puzzle.

Reviewers: #kde_games, ltoscano

Reviewed By: ltoscano

Subscribers: ltoscano, #kde_games

Differential Revision: https://phabricator.kde.org/D7566