Safely close database connections and delete backends

Also fix NewClosure leak caused by disconnected object signals

src/subsonic/subsonicbaserequest.cpp

@@ -50,7 +50,7 @@ SubsonicBaseRequest::~SubsonicBaseRequest() {
 
   while (!replies_.isEmpty()) {
     QNetworkReply *reply = replies_.takeFirst();
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     if (reply->isRunning()) reply->abort();
     reply->deleteLater();
   }

src/subsonic/subsonicrequest.cpp

@@ -71,7 +71,7 @@ SubsonicRequest::~SubsonicRequest() {
 
   while (!album_cover_replies_.isEmpty()) {
     QNetworkReply *reply = album_cover_replies_.takeFirst();
-    disconnect(reply, 0, nullptr, 0);
+    disconnect(reply, 0, this, 0);
     if (reply->isRunning()) reply->abort();
     reply->deleteLater();
   }

src/subsonic/subsonicservice.cpp

@@ -95,7 +95,14 @@ SubsonicService::SubsonicService(Application *app, QObject *parent)
 }
 
 SubsonicService::~SubsonicService() {
-  collection_backend_->deleteLater();
+  delete collection_backend_;
+}
+
+void SubsonicService::Exit() {
+
+  connect(collection_backend_, SIGNAL(ExitFinished()), this, SIGNAL(ExitFinished()));
+  collection_backend_->ExitAsync();
+
 }
 
 void SubsonicService::ShowConfig() {
@@ -317,8 +324,8 @@ void SubsonicService::CheckConfiguration() {
 
 void SubsonicService::ResetSongsRequest() {
 
-  if (songs_request_.get()) {
-    disconnect(songs_request_.get(), 0, nullptr, 0);
+  if (songs_request_.get()) {  // WARNING: Don't disconnect everything. NewClosure() relies on destroyed()!!!
+    disconnect(songs_request_.get(), 0, this, 0);
     disconnect(this, 0, songs_request_.get(), 0);
     songs_request_.reset();
   }

src/subsonic/subsonicservice.h

@@ -60,6 +60,7 @@ class SubsonicService : public InternetService {
   static const Song::Source kSource;
 
   void ReloadSettings();
+  void Exit();
 
   Application *app() { return app_; }