journal: Skip data objects with invalid offsets

journal: Skip data objects with invalid offsets

We already skip invalid objects, but don't yet skip invalid offsets.
Let's skip these as well to improve robustness when we're dealing with
corrupted journals.

Before:

```
➜  systemd git:(main) build/journalctl -r -n 5 --file ~/Downloads/system@0005d2b275abaaf8-f243a2818cb39b98.journal_
Failed to get journal fields: Cannot assign requested address
-- No entries --
```

After:

```
➜  systemd git:(main) ✗ build/journalctl -r -n 5 --file ~/Downloads/system@0005d2b275abaaf8-f243a2818cb39b98.journal_
Dec 09 08:32:38 snowball3 NetworkManager[911]: <info>  [1639038758.1464] device (wlp1s0): supplicant interface state: scanning -> authenticating
Dec 09 08:32:38 snowball3 kernel: wlp1s0: send auth to ec:a9:40:79:fb:ad (try 1/3)
Dec 09 08:32:38 snowball3 kernel: wlp1s0: authenticate with ec:a9:40:79:fb:ad
Dec 09 08:32:38 snowball3 wpa_supplicant[1003]: wlp1s0: SME: Trying to authenticate with ec:a9:40:79:fb:ad (SSID='UPC949397B' freq=5500 MHz)
```