TagFile: pass reference instead of pointer

src/SongUpdate.cxx

@@ -89,7 +89,7 @@ Song::UpdateFile()
 
 	TagBuilder tag_builder;
 	if (!tag_file_scan(path_fs,
-			   &full_tag_handler, &tag_builder))
+			   full_tag_handler, &tag_builder))
 		return false;
 
 	if (tag_builder.IsEmpty())

src/TagFile.cxx

@@ -80,11 +80,9 @@ public:
 };
 
 bool
-tag_file_scan(Path path_fs,
-	      const struct tag_handler *handler, void *handler_ctx)
+tag_file_scan(Path path_fs, const tag_handler &handler, void *handler_ctx)
 {
 	assert(!path_fs.IsNull());
-	assert(handler != nullptr);
 
 	/* check if there's a suffix and a plugin */
 
@@ -92,7 +90,7 @@ tag_file_scan(Path path_fs,
 	if (suffix == nullptr)
 		return false;
 
-	TagFileScan tfs(path_fs, suffix, *handler, handler_ctx);
+	TagFileScan tfs(path_fs, suffix, handler, handler_ctx);
 	return decoder_plugins_try([&](const DecoderPlugin &plugin){
 			return tfs.Scan(plugin);
 		});

src/TagFile.hxx

@@ -33,7 +33,6 @@ struct tag_handler;
  * found)
  */
 bool
-tag_file_scan(Path path,
-	      const tag_handler *handler, void *handler_ctx);
+tag_file_scan(Path path, const tag_handler &handler, void *handler_ctx);
 
 #endif

src/command/FileCommands.cxx

@@ -114,7 +114,7 @@ handle_read_comments(Client &client, gcc_unused int argc, char *argv[])
 		return CommandResult::ERROR;
 	}
 
-	if (!tag_file_scan(path_fs, &print_comment_handler, &client)) {
+	if (!tag_file_scan(path_fs, print_comment_handler, &client)) {
 		command_error(client, ACK_ERROR_NO_EXIST,
 			      "Failed to load file");
 		return CommandResult::ERROR;

src/playlist/EmbeddedCuePlaylistPlugin.cxx

@@ -103,7 +103,7 @@ embcue_playlist_open_uri(const char *uri,
 
 	const auto playlist = new EmbeddedCuePlaylist();
 
-	tag_file_scan(path_fs, &embcue_tag_handler, playlist);
+	tag_file_scan(path_fs, embcue_tag_handler, playlist);
 	if (playlist->cuesheet.empty()) {
 		tag_ape_scan2(path_fs, &embcue_tag_handler, playlist);
 		if (playlist->cuesheet.empty())