decoder/flac: pass FLAC__Metadata_Chain* to FLACMetadataIterator ctor

src/decoder/plugins/FlacMetadata.cxx

@@ -163,7 +163,7 @@ flac_vorbis_comments_to_tag(const FLAC__StreamMetadata_VorbisComment *comment)
 void
 FlacMetadataChain::Scan(TagHandler &handler) noexcept
 {
-	FLACMetadataIterator iterator(*this);
+	FLACMetadataIterator iterator(chain);
 
 	do {
 		FLAC__StreamMetadata *block = iterator.GetBlock();

src/decoder/plugins/FlacMetadata.hxx

@@ -91,10 +91,9 @@ class FLACMetadataIterator {
 public:
 	FLACMetadataIterator():iterator(::FLAC__metadata_iterator_new()) {}
 
-	FLACMetadataIterator(FlacMetadataChain &chain)
+	FLACMetadataIterator(FLAC__Metadata_Chain *chain)
 		:iterator(::FLAC__metadata_iterator_new()) {
-		::FLAC__metadata_iterator_init(iterator,
-					       (FLAC__Metadata_Chain *)chain);
+		::FLAC__metadata_iterator_init(iterator, chain);
 	}
 
 	~FLACMetadataIterator() {