Fix pg_waldump to exit cleanly at end of WAL - Mailing list pgsql-hackers

Hi Hackers,

I noticed a problem with pg_waldump. When "-e" is not specified, or given a bigger number beyond the current LSN, pg_dump always print an error message like:

```

chaol@ChaodeMacBook-Air cndb % pg_waldump -p pg_wal -s 0/2980DE10 -e 0/2980E680
<...omit some outputs...>
rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 0/2980E468, prev 0/2980E3F0, desc: RUNNING_XACTS nextXid 866 latestCompletedXid 865 oldestRunningXid 866
pg_waldump: error: error in WAL record at 0/2980E468: invalid record length at 0/2980E4A0: expected at least 24, got 0

```

The error message is kinda misleading and unnecessary. So I created a fix.

From the code comment in pg_waldump.c, the same change should be applied to pg_walinspect. If this patch is accepted, I will then work on pg_walinspect as well.

Best regards,