reftable: release name on reftable_reader_new() error

If block_source_read_block() or parse_footer() fail, we leak the "name"
member of struct reftable_reader in reftable_reader_new().  Release it.

Reported by: H Z <shiyuyuranzh@gmail.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

reftable/reader.c

@@ -666,6 +666,8 @@ done:
 	reftable_block_done(&footer);
 	reftable_block_done(&header);
 	if (err) {
+		if (r)
+			reftable_free(r->name);
 		reftable_free(r);
 		block_source_close(source);
 	}