refs/reftable: fix leak when copying reflog fails

When copying a ref with the reftable backend we also copy the
corresponding log records. When seeking the first log record that we're
about to copy fails though we directly return from `write_copy_table()`
without doing any cleanup, leaking several allocated data structures.

Fix this by exiting via our common cleanup logic instead.

Reported-by: Jeff King <[email protected]> via Coverity
Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

refs/reftable-backend.c

@@ -1503,7 +1503,7 @@ static int write_copy_table(struct reftable_writer *writer, void *cb_data)
 	 */
 	ret = reftable_merged_table_seek_log(mt, &it, arg->oldname);
 	if (ret < 0)
-		return ret;
+		goto done;
 
 	while (1) {
 		ret = reftable_iterator_next_log(&it, &old_log);