provide default scheme file for !shown cases

--when the colorizer informs the applets to paint
themselves based on the current plasma theme some
of them (e.g. Window Buttons) may still need access
to that color palette through the schemeFile variable.
To support also this case Latte provides the default
theme scheme file at all cases.

containment/package/contents/ui/colorizer/Manager.qml

@@ -87,8 +87,8 @@ Loader{
     readonly property color buttonFocusColor: theme.buttonFocusColor
 
     readonly property string scheme: {
-        if (applyTheme===theme) {
-            return applyTheme.defaultTheme.schemeFile;
+        if (applyTheme===theme || !mustBeShown) {
+            return themeExtended.defaultTheme.schemeFile;
         }
 
         return applyTheme.schemeFile;