[platforms/x11] Fix valigrind warning copying window icon for windowed mode

Summary:
windowIcon.pixmap().bits() creates and deletes the QPixmap object.

Which means data is dangling when we call m_winInfo->setIcon()

Surprisingly harmless in real life.

Test Plan: Reran kwin_wayland on X11 with valigrind

Reviewers: #kwin, apol

Reviewed By: apol

Subscribers: zzag, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D28667

plugins/platforms/x11/windowed/x11windowed_output.cpp

@@ -104,7 +104,8 @@ void X11WindowedOutput::init(const QPoint &logicalPosition, const QSize &pixelSi
             return;
         }
         NETIcon icon;
-        icon.data = windowIcon.pixmap(size).toImage().bits();
+        QImage windowImage = windowIcon.pixmap(size).toImage();
+        icon.data = windowImage.bits();
         icon.size.width = size.width();
         icon.size.height = size.height();
         m_winInfo->setIcon(icon, false);