D7190: Don't complain the knsregistry file is not present before it's useful

[Aleix Pol Gonzalez]

apol created this revision.
Restricted Application added a project: Frameworks.
Restricted Application added a subscriber: Frameworks.

REVISION SUMMARY
  Only consider it an error if the knsregistry file is present but can't
  be written on.

REPOSITORY
  R304 KNewStuff

BRANCH
  master

REVISION DETAIL
  https://phabricator.kde.org/D7190

AFFECTED FILES
  src/core/cache.cpp

To: apol, leinir
Cc: #frameworks