We never check if a destination directory is writable, while doing an ExtractJob.
We can do this check only once, in ExtractJob::doWork(), instead of doing it
in each plugin's copyFiles(). This way we don't even start a cli process which
we already know is going to fail.
The only downside is that in batch mode (ark -b) the error message is displayed
twice, once in a KMessageBox and once in a Plasma notification.
BUG: 192219
FIXED-IN: 15.12.0