Debugger: Keep secondary dialogs on top of the main window

Change-Id: I1f4283a5727db976d999d4cf4c7e444de8592566
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/plugins/debugger/cdb/cdbengine.cpp

@@ -207,7 +207,7 @@ static QMessageBox *
 nonModalMessageBox(QMessageBox::Icon icon, const QString &title, const QString &text)
 {
     QMessageBox *mb = new QMessageBox(icon, title, text, QMessageBox::Ok,
-                                      debuggerCore()->mainWindow());
+                                      Core::ICore::mainWindow());
     mb->setAttribute(Qt::WA_DeleteOnClose);
     mb->show();
     return mb;