do not incorrectly split spaces in paths of duplicate results

Summary:
use kcoreaddons to split fdupes output. fdupes outputs
/space\ inbetween/x.svg /space\ inbetween/y.svg
as dupe result, which, if we split blindly for space, we'll split into 4
pieces instead of 2.
splitting the argument string using escape rules via kshell gives us
correct splitting by taking into account the escaped spaces.

unfortunately qregex doesn't seem to support negative lookbehind
expressions, or we could solve this with a (?<!\\\\) instead of having
to use kshell.

Test Plan: test output is lovely again

Reviewers: dfaure, apol

Reviewed By: apol

Subscribers: Frameworks

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D9781