Don't set a custom palette if we have the same palette as the currently active one
Summary: Caused some icons not be colored correctly
Test Plan: Close KWrite with unsaved changes, all icons should be colored correctly
Reviewers: broulik, ngraham
Reviewed By: broulik, ngraham
Subscribers: ngraham, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D28830