ensure winId() not called on non-native widgets

Summary:
if we do that, window will be corrupted

BUG: 412675

Test Plan: Use Kate, change color theme on a second screen with scaling

Reviewers: #frameworks, dfaure

Reviewed By: dfaure

Subscribers: broulik, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D24442

src/kstyle/kstyle.cpp

@@ -104,7 +104,8 @@ bool ColorSchemeFilter::eventFilter(QObject *object, QEvent *event)
 
 void ColorSchemeFilter::installColorScheme(QWidget *w)
 {
-    if (!w || !w->isTopLevel()) {
+    // ensure we don't call winId() on non-native widgets, bug 412675
+    if (!w || !w->isTopLevel() || !w->windowHandle()) {
         return;
     }
 #if HAVE_X11