Playlist: copy stream tags from the PlayerThread

Finally restores an important feature that has been broken for several
months when the PlayerThread started working with Song copies instead
of pointers to the Queue's Song instances (commit e96779d).

src/PlayerThread.cxx

@@ -335,6 +335,8 @@ Player::WaitForDecoder()
 		return false;
 	}
 
+	pc.ClearTaggedSong();
+
 	if (song != nullptr)
 		song->Free();
 
@@ -684,7 +686,7 @@ Player::ProcessCommand()
 }
 
 static void
-update_song_tag(Song *song, const Tag &new_tag)
+update_song_tag(player_control &pc, Song *song, const Tag &new_tag)
 {
 	if (song->IsFile())
 		/* don't update tags of local files, only remote
@@ -696,6 +698,8 @@ update_song_tag(Song *song, const Tag &new_tag)
 
 	delete old_tag;
 
+	pc.LockSetTaggedSong(*song);
+
 	/* the main thread will update the playlist version when he
 	   receives this event */
 	GlobalEvents::Emit(GlobalEvents::TAG);
@@ -722,7 +726,7 @@ play_chunk(player_control &pc,
 	assert(chunk->CheckFormat(format));
 
 	if (chunk->tag != nullptr)
-		update_song_tag(song, *chunk->tag);
+		update_song_tag(pc, song, *chunk->tag);
 
 	if (chunk->IsEmpty()) {
 		buffer.Return(chunk);
@@ -1077,6 +1081,8 @@ Player::Run()
 
 	pc.Lock();
 
+	pc.ClearTaggedSong();
+
 	if (queued) {
 		assert(pc.next_song != nullptr);
 		pc.next_song->Free();