Fix a relcache reference leak in reorderbuffer.c

Hi,

While working on a feature patch that I’m going to post soon, I noticed a small issue in reorderbuffer.c. In the REORDER_BUFFER_CHANGE_TRUNCATE branch of ReorderBufferProcessTXN(), some opened relations might be skipped without being closed, leading to leaked relcache references.

The relevant code is:
```
relations = palloc0_array(Relation, nrelids);
for (i = 0; i < nrelids; i++)
{
Oid relid = change->data.truncate.relids[i];
Relation rel;

rel = RelationIdGetRelation(relid);

if (!RelationIsValid(rel))
elog(ERROR, "could not open relation with OID %u", relid);

if (!RelationIsLogicallyLogged(rel))
continue; <===== it should close rel before skipping it

relations[nrelations++] = rel;
}

/* Apply the truncate. */
ReorderBufferApplyTruncate(rb, txn, nrelations,
relations, change,
streaming);

for (i = 0; i < nrelations; i++)
RelationClose(relations[i]);
```

In the loop, each relation that is appended to relations is closed after the loop. However, when RelationIsLogicallyLogged(rel) returns false, the relation is skipped without being closed, causing the leak.

The attached patch makes a small fix to close the relation before continuing.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/