Windows theme: don't refresh anything unless theme really changed

Refreshing the global theme may be expensive for large scale applications, and even if Windows sent corresponding message,
it may be triggered by many reasons, not just the system theme,
so no matter what we'd better add an extra check.

Pick-to: 6.9
Change-Id: I70847aa54fb4af37c81855a62330a4bce31ff104
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

src/plugins/platforms/windows/qwindowstheme.cpp

@@ -604,16 +604,16 @@ void QWindowsTheme::handleSettingsChanged()
     const auto newColorScheme = effectiveColorScheme();
     const bool colorSchemeChanged = newColorScheme != oldColorScheme;
     s_colorScheme = newColorScheme;
+    if (!colorSchemeChanged)
+        return;
     auto integration = QWindowsIntegration::instance();
     integration->updateApplicationBadge();
     if (integration->darkModeHandling().testFlag(QWindowsApplication::DarkModeStyle)) {
         QWindowsTheme::instance()->refresh();
         QWindowSystemInterface::handleThemeChange<QWindowSystemInterface::SynchronousDelivery>();
     }
-    if (colorSchemeChanged) {
-        for (QWindowsWindow *w : std::as_const(QWindowsContext::instance()->windows()))
-            w->setDarkBorder(s_colorScheme == Qt::ColorScheme::Dark);
-    }
+    for (QWindowsWindow *w : std::as_const(QWindowsContext::instance()->windows()))
+        w->setDarkBorder(s_colorScheme == Qt::ColorScheme::Dark);
 }
 
 void QWindowsTheme::clearPalettes()