Avoid pointless config parse in ksplash

Summary:
Due to the nature of cascading configs we have already loaded and parsed
kdeglobals, it's wasteful to do it again. Especially in ksplash where startup time is important.

Test Plan:
Changed lnf to org.obnosim.tweak.desktop which contains a new splash
Logged out and back in. Still got a different splash.

Reviewers: #plasma

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D11923