Fix off-by-one in XLogRecordMaxSize check.

pg_logical_emit_message(false, '_', repeat('x', 1069547465)) failed with
self-contradictory message "WAL record would be 1069547520 bytes (of
maximum 1069547520 bytes)".  There's no particular benefit from allowing
or denying one byte in either direction; XLogRecordMaxSize could rise a
few megabytes without trouble.  Hence, this is just for cleanliness.
Back-patch to v16, where this check first appeared.

Author: nmisch

src/backend/access/transam/xloginsert.c

@@ -900,7 +900,7 @@ XLogRecordAssemble(RmgrId rmid, uint8 info,
 	 * not emit records larger than the sizes advertised to be supported. This
 	 * cap is based on DecodeXLogRecordRequiredSpace().
 	 */
-	if (total_len >= XLogRecordMaxSize)
+	if (total_len > XLogRecordMaxSize)
 		ereport(ERROR,
 				(errmsg_internal("oversized WAL record"),
 				 errdetail_internal("WAL record would be %llu bytes (of maximum %u bytes); rmid %u flags %u.",