VCS: Fix possible crash on shutdown

Similar to how it is done for the WindowTitleAdditionHandler and
SessionTitleHandler.

Fixes: QTCREATORBUG-27048
Change-Id: Ic8c140b99c7c6edbc43bed5f1b9275b4af5ce831
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/vcsbase/vcsbaseplugin.cpp

@@ -197,6 +197,7 @@ class StateListener : public QObject
 
 public:
     explicit StateListener(QObject *parent);
+    ~StateListener();
 
     static QString windowTitleVcsTopic(const QString &filePath);
 
@@ -221,10 +222,14 @@ StateListener::StateListener(QObject *parent) : QObject(parent)
     connect(SessionManager::instance(), &SessionManager::startupProjectChanged,
             this, &StateListener::slotStateChanged);
 
-
     EditorManager::setWindowTitleVcsTopicHandler(&StateListener::windowTitleVcsTopic);
 }
 
+StateListener::~StateListener()
+{
+    EditorManager::setWindowTitleVcsTopicHandler({});
+}
+
 QString StateListener::windowTitleVcsTopic(const QString &filePath)
 {
     FilePath searchPath;