cleanup Audio bg threads in cleanupBeforeQuit

interface/src/Application.cpp

@@ -1785,7 +1785,8 @@ void Application::cleanupBeforeQuit() {
 
     // FIXME: something else is holding a reference to AudioClient,
     // so it must be explicitly synchronously stopped here
-    QMetaObject::invokeMethod(DependencyManager::get<AudioClient>().data(), "stop", Qt::BlockingQueuedConnection);
+    QMetaObject::invokeMethod(DependencyManager::get<AudioClient>().data(),
+        "cleanupBeforeQuit", Qt::BlockingQueuedConnection);
 
     // destroy Audio so it and its threads have a chance to go down safely
     // this must happen after QML, as there are unexplained audio crashes originating in qtwebengine

libraries/audio-client/src/AudioClient.cpp

@@ -254,15 +254,24 @@ AudioClient::~AudioClient() {
 }
 
 void AudioClient::customDeleter() {
-    stop(); // synchronously
+    deleteLater();
+}
 
-    static_cast<BackgroundThread*>(_checkDevicesThread)->join();
-    delete _checkDevicesThread;
+void AudioClient::cleanupBeforeQuit() {
+    // FIXME: this should be put in customDeleter, but there is still a reference to this when it is called,
+    //        so this must be explicitly, synchronously stopped
 
-    static_cast<BackgroundThread*>(_localInjectorsThread)->join();
-    delete _localInjectorsThread;
+    stop();
 
-    deleteLater(); // asynchronously
+    if (_checkDevicesThread) {
+        static_cast<BackgroundThread*>(_checkDevicesThread)->join();
+        delete _checkDevicesThread;
+    }
+
+    if (_localInjectorsThread) {
+        static_cast<BackgroundThread*>(_localInjectorsThread)->join();
+        delete _localInjectorsThread;
+    }
 }
 
 void AudioClient::handleMismatchAudioFormat(SharedNodePointer node, const QString& currentCodec, const QString& recievedCodec) {

libraries/audio-client/src/AudioClient.h

@@ -158,6 +158,7 @@ public:
 public slots:
     void start();
     void stop();
+    void cleanupBeforeQuit();
 
     void handleAudioEnvironmentDataPacket(QSharedPointer<ReceivedMessage> message);
     void handleAudioDataPacket(QSharedPointer<ReceivedMessage> message);