archive/iso9660: skip empty filenames

Aparently, libcdio sometimes returns empty filenames, causing MPD
crashes.  This shouldn't really happen, and I consider this a libcdio
bug - but if it happens, people blame MPD, so let's add a check.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/776

NEWS

@@ -1,4 +1,6 @@
 ver 0.21.21 (not yet released)
+* archive
+  - iso9660: skip empty file names to work around libcdio bug
 * decoder
   - gme: ignore empty tags
 * output

src/archive/plugins/Iso9660ArchivePlugin.cxx

@@ -28,6 +28,7 @@
 #include "input/InputStream.hxx"
 #include "fs/Path.hxx"
 #include "util/RuntimeError.hxx"
+#include "util/StringCompare.hxx"
 
 #include <cdio/iso9660.h>
 
@@ -93,7 +94,9 @@ Iso9660ArchiveFile::Visit(char *path, size_t length, size_t capacity,
 		auto *statbuf = (iso9660_stat_t *)
 			_cdio_list_node_data(entnode);
 		const char *filename = statbuf->filename;
-		if (PathTraitsUTF8::IsSpecialFilename(filename))
+		if (StringIsEmpty(filename) ||
+		    PathTraitsUTF8::IsSpecialFilename(filename))
+			/* skip empty names (libcdio bug?) */
 			/* skip special names like "." and ".." */
 			continue;