Return QPalette() if we have no custom palette
If the app colorscheme is changed (for example by KColorSchemeManager), mPalette can go out of sync with the palette that is actually used for coloring icons when no custom palette is set.
If the app colorscheme is changed (for example by KColorSchemeManager), mPalette can go out of sync with the palette that is actually used for coloring icons when no custom palette is set.