SongUpdate: use OpenArchiveInputStream() to open archive file

Don't pass Path::c_str() to tag_stream_scan() which requires a UTF-8
string.

src/TagArchive.cxx

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2003-2015 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "TagArchive.hxx"
+#include "TagStream.hxx"
+#include "fs/Path.hxx"
+#include "util/Error.hxx"
+#include "input/InputStream.hxx"
+#include "input/plugins/ArchiveInputPlugin.hxx"
+#include "thread/Cond.hxx"
+
+#include <assert.h>
+
+bool
+tag_archive_scan(Path path, const tag_handler &handler, void *handler_ctx)
+{
+	assert(!path.IsNull());
+
+	Mutex mutex;
+	Cond cond;
+	auto *is = OpenArchiveInputStream(path, mutex, cond, IgnoreError());
+	if (is == nullptr)
+		return false;
+
+	bool result = tag_stream_scan(*is, handler, handler_ctx);
+	delete is;
+	return result;
+}