Fix code style and errors

src/core/songloader.cpp

@@ -257,7 +257,7 @@ void SongLoader::LoadLocalAsync(const QString &filename) {
     cue.open(QIODevice::ReadOnly);
 
     SongList song_list = cue_parser_->Load(&cue, matching_cue, QDir(filename.section('/', 0, -2)));
-    for (Song song: song_list){
+    for (const Song &song : song_list) {
       if (song.is_valid()) songs_ << song;
     }
     return;