AlbumCoverLoader: Use own NetworkAccessManager instance

Since AlbumCoverLoader runs in it's own thread.

src/core/application.cpp

@@ -149,7 +149,7 @@ class ApplicationImpl {
           return cover_providers;
         }),
         album_cover_loader_([app]() {
-          AlbumCoverLoader *loader = new AlbumCoverLoader(app->network(), app);
+          AlbumCoverLoader *loader = new AlbumCoverLoader(app);
           app->MoveToNewThread(loader);
           return loader;
         }),

src/covermanager/albumcoverloader.cpp

@@ -53,9 +53,9 @@
 #include "albumcoverloaderresult.h"
 #include "albumcoverimageresult.h"
 
-AlbumCoverLoader::AlbumCoverLoader(NetworkAccessManager *network, QObject *parent)
+AlbumCoverLoader::AlbumCoverLoader(QObject *parent)
     : QObject(parent),
-      network_(network),
+      network_(new NetworkAccessManager(this)),
       stop_requested_(false),
       load_image_async_id_(1),
       save_image_async_id_(1),

src/covermanager/albumcoverloader.h

@@ -51,7 +51,7 @@ class AlbumCoverLoader : public QObject {
   Q_OBJECT
 
  public:
-  explicit AlbumCoverLoader(NetworkAccessManager *network, QObject *parent = nullptr);
+  explicit AlbumCoverLoader(QObject *parent = nullptr);
 
   enum class State {
     None,