Mark that shutdown has started and don't start any new thread anymore

Amends cb5977fbad

Task-number: QTCREATORBUG-25318
Change-Id: I650389d53571724fe1ec4e299d7d3d8cf4a24061
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/locator/locator.cpp

@@ -171,6 +171,7 @@ bool Locator::delayedInitialize()
 
 void Locator::aboutToShutdown()
 {
+    m_shuttingDown = true;
     m_refreshTimer.stop();
     if (m_refreshTask.isRunning()) {
         m_refreshTask.cancel();
@@ -384,6 +385,9 @@ void Locator::setRefreshInterval(int interval)
 
 void Locator::refresh(QList<ILocatorFilter *> filters)
 {
+    if (m_shuttingDown)
+        return;
+
     if (m_refreshTask.isRunning()) {
         m_refreshTask.cancel();
         // this is not ideal because some of the previous filters might have finished, but we

src/plugins/coreplugin/locator/locator.h

@@ -76,6 +76,7 @@ private:
 
     LocatorData *m_locatorData = nullptr;
 
+    bool m_shuttingDown = false;
     bool m_settingsInitialized = false;
     QList<ILocatorFilter *> m_filters;
     QList<ILocatorFilter *> m_customFilters;