Ensure that update script does not overwrite settings

The upgrade script changed to thumbnails layout in case that there
has not been any settings for BoxSwitch effect stored in the config
file.

REVIEW: 104129

data/update_tabbox_qml_settings.cpp

@@ -46,9 +46,11 @@ int main( int argc, char* argv[] )
     KComponentData inst( &about );
     Q_UNUSED( KGlobal::locale() ); // jump-start locales to get to translated descriptions
     KConfig config("kwinrc");
+    KConfigGroup plugins = config.group("Plugins");
+    const bool boxSwitchEnabled = plugins.readEntry<bool>("kwin4_effect_boxswitchEnabled", true);
     KConfigGroup boxswitch = config.group("Effect-BoxSwitch");
-    const bool boxSwitchPrimary = boxswitch.readEntry<bool>("TabBox", true);
-    const bool boxSwitchAlternative = boxswitch.readEntry<bool>("TabBoxAlternative", false);
+    const bool boxSwitchPrimary = boxSwitchEnabled && boxswitch.hasKey("TabBox") && boxswitch.readEntry<bool>("TabBox", true);
+    const bool boxSwitchAlternative = boxSwitchEnabled && boxswitch.hasKey("TabBoxAlternative") && boxswitch.readEntry<bool>("TabBoxAlternative", false);
     boxswitch.writeEntry("TabBox", false);
     boxswitch.writeEntry("TabBoxAlternative", false);
     boxswitch.sync();