Fix the error overlay shown on other kcms

Nate Graham requested to merge work/cherry-pick-e36fc3c9 into Plasma/5.27

After the error overlay was shown, when visiting certain other kcm pages (for example, kde connect), it was still shown. Also fixes the overlay overlapping the bottom buttons.

BUG: 424531

(cherry picked from commit e36fc3c9)

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