KWin decorations: Fix KCM not refreshing after clicking "Use"-button in KNS dialog

Alexander Lohnaurequested to merge
work/kcm_refresh into master

CCBUG: 448749

With frameworks/knewstuff!162 (merged), we do not have to compare ints anymore. But for backportability we have to stick with that for now.

@vladz @ngraham

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