Fix possible crash in tablesync worker.

Commit c3afe8c added a new password_required option but forgot that you
need database access to check whether an arbitrary role ID is a superuser.

Commit e7e7da2 fixed a similar bug in apply worker, and this patch
fixes a similar bug in tablesync worker.

Author: Hou Zhijie
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/OS0PR01MB571607F5A9D723755268D36294759@OS0PR01MB5716.jpnprd01.prod.outlook.com

Author: Amit Kapila

src/backend/replication/logical/tablesync.c

@@ -1262,6 +1262,12 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
 	relstate = GetSubscriptionRelState(MyLogicalRepWorker->subid,
 									   MyLogicalRepWorker->relid,
 									   &relstate_lsn);
+
+	/* Is the use of a password mandatory? */
+	must_use_password = MySubscription->passwordrequired &&
+		!superuser_arg(MySubscription->owner);
+
+	/* Note that the superuser_arg call can access the DB */
 	CommitTransactionCommand();
 
 	SpinLockAcquire(&MyLogicalRepWorker->relmutex);
@@ -1288,10 +1294,6 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
 									slotname,
 									NAMEDATALEN);
 
-	/* Is the use of a password mandatory? */
-	must_use_password = MySubscription->passwordrequired &&
-		!superuser_arg(MySubscription->owner);
-
 	/*
 	 * Here we use the slot name instead of the subscription name as the
 	 * application_name, so that it is different from the leader apply worker,