desktop-shell: fix the crash while clicking TRANSIENT_INACTIVE window

It is pretty easy to replicate this bug by involving a Qt Window with
Qt::WindowTransparentForInput flag.

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    QDialog d1(&w, Qt::WindowTransparentForInput);
    d1.show();

    return a.exec();
}

Click d1 dialog, weston will crash due to NULL==shruf.

Signed-off-by: Barry Song <barry.song@navico.com>
2 jobs for fix-transient-crash in 1 minute and 49 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Container Prep
passed #245564
container_prep

00:01:13

 
  Build
passed #245565
build-native-meson

00:00:36