Major Version Upgrade failure due to orphan roles entries in catalog

Hi,

We have identified an issue causing upgrade failures. The following steps
detail how to reproduce the issue:

*Create an orphan role entry*

/* Postgres version:: PostgreSQL 16.6 */
/* The same can be reproduced in version 17 as well */

create role my_group;
create role dropped_member;
begin;
grant my_group to dropped_member;
OTHER SESSION: drop role dropped_member;
BACK IN ORIGINAL SESSION:
commit;

*Upgrade to Postgres v17*

And the upgrade fails with an error :

*GRANT "my_group" TO "" WITH INHERIT TRUE GRANTED BY "postgres";ERROR:
zero-length delimited identifier at or near """"*

The issue seems to be coming from pg_dumpall for building grants during
pg_upgrade.

https://github.com/postgres/postgres/blob/master/src/bin/pg_dump/pg_dumpall.c#L992

-Virender