libFLAC: fix leak in metadata_iterators.c

node isn't cleared if metadata reading fails in
read_metadata_block_header_cb.
diff --git a/libFLAC/metadata_iterators.c b/libFLAC/metadata_iterators.c
index 15362f7..8b9dbec 100644
--- a/libFLAC/metadata_iterators.c
+++ b/libFLAC/metadata_iterators.c
@@ -1217,6 +1217,7 @@
 			}
 
 			if(!read_metadata_block_header_cb_(handle, read_cb, &is_last, &type, &length)) {
+				node_delete_(node);
 				chain->status = FLAC__METADATA_CHAIN_STATUS_READ_ERROR;
 				return false;
 			}