D28760: KSettings::Dialog: avoid duplicate entries due cascading $XDG_DATA_DIRS

[David Faure]

dfaure added a reviewer: svuorela.

REPOSITORY
  R295 KCMUtils

REVISION DETAIL
  https://phabricator.kde.org/D28760

To: dfaure, apol, broulik, davidedmundson, kossebau, svuorela
Cc: kde-frameworks-devel, LeGast00n, cblack, michaelh, ngraham, bruns