Fix really terrible code

plugins/systemvolume/systemvolumeplugin-win.cpp

@@ -227,6 +227,15 @@ SystemvolumePlugin::SystemvolumePlugin(QObject *parent, const QVariantList &args
 SystemvolumePlugin::~SystemvolumePlugin()
 {
     if (valid) {
+        QSet<IAudioEndpointVolume*> endpoints;
+        for (auto &entry : sinkList.toStdMap()) {
+            endpoint->UnRegisterControlChangeNotify(entry.second);
+            endpoint->Release();
+            endpoints.insert(entry.first);
+        }
+        for (IAudioEndpointVolume* endpoint : endpoints) {
+            endpoint->Release();
+        }
         deviceEnumerator->UnregisterEndpointNotificationCallback(deviceCallback);
         deviceEnumerator->Release();
         deviceEnumerator = nullptr;
@@ -404,14 +413,12 @@ bool SystemvolumePlugin::receivePacket(const NetworkPacket &np)
     } else {
         QString name = np.get<QString>(QStringLiteral("name"));
 
-        if (sinkList.contains(name)) {
-            // unregister ControlChangeNotify before doing any changes to a sink
-            HRESULT unregisterSuccess = E_POINTER;
         auto sinkListIterator = this->sinkList.find(name);
+        if (sinkListIterator != this->sinkList.end()) {
             auto &sink = sinkListIterator.value();
-            if (!(sinkListIterator == this->sinkList.end())) {
-                unregisterSuccess = sink.first->UnregisterControlChangeNotify(sink.second);
-            }
+
+            // unregister ControlChangeNotify before doing any changes to a sink
+            HRESULT unregisterSuccess = sink.first->UnregisterControlChangeNotify(sink.second);
 
             if (np.has(QStringLiteral("volume"))) {
                 float currentVolume;