Apply patch by Anssi Hannula, to fix KConfigIniBackend::isWritable

... when the parent directory doesn't exist.

cdUp() fails when the parent directory doesn't exist, causing
isWritable() to bail out and return false without checking further
parent directories.

Fix that by walking through the tree using QFileInfo::absolutePath()
instead.

https://bugs.mageia.org/show_bug.cgi?id=3601#c10

REVIEW: 103577
FIXED-IN: 4.8.1