Use std::bind in QtConcurrent::run() to fix compile with Qt 6

src/playlist/playlist.cpp

@@ -1314,7 +1314,7 @@ void Playlist::Restore() {
   collection_items_by_id_.clear();
 
   cancel_restore_ = false;
-  QFuture<QList<PlaylistItemPtr>> future = QtConcurrent::run(backend_, &PlaylistBackend::GetPlaylistItems, id_);
+  QFuture<QList<PlaylistItemPtr>> future = QtConcurrent::run(std::bind(&PlaylistBackend::GetPlaylistItems, backend_, id_));
   NewClosure(future, this, SLOT(ItemsLoaded(QFuture<PlaylistItemList>)), future);
 
 }
@@ -1353,7 +1353,7 @@ void Playlist::ItemsLoaded(QFuture<PlaylistItemList> future) {
 
   // Should we gray out deleted songs asynchronously on startup?
   if (greyout) {
-    QtConcurrent::run(this, &Playlist::InvalidateDeletedSongs);
+    (void)QtConcurrent::run(std::bind(&Playlist::InvalidateDeletedSongs, this));
   }
 
   emit PlaylistLoaded();

src/playlist/playlistmanager.cpp

@@ -21,6 +21,7 @@
 #include "config.h"
 
 #include <memory>
+#include <functional>
 
 #include <QtGlobal>
 #include <QObject>
@@ -211,7 +212,7 @@ void PlaylistManager::Save(int id, const QString &filename, Playlist::Path path_
   }
   else {
     // Playlist is not in the playlist manager: probably save action was triggered from the left side bar and the playlist isn't loaded.
-    QFuture<QList<Song>> future = QtConcurrent::run(playlist_backend_, &PlaylistBackend::GetPlaylistSongs, id);
+    QFuture<QList<Song>> future = QtConcurrent::run(std::bind(&PlaylistBackend::GetPlaylistSongs, playlist_backend_, id));
     NewClosure(future, this, SLOT(ItemsLoadedForSavePlaylist(QFuture<SongList>, QString, Playlist::Path)), future, filename, path_type);
   }
 

src/playlist/songloaderinserter.cpp

@@ -83,7 +83,7 @@ void SongLoaderInserter::Load(Playlist *destination, int row, bool play_now, boo
     deleteLater();
   }
   else {
-    QtConcurrent::run(this, &SongLoaderInserter::AsyncLoad);
+    (void)QtConcurrent::run([=]{ AsyncLoad(); });
   }
 }