Check whether $this->batch is empty before running unserialize to prevent repeated errors

I'm moving this to the Feeds queue because it's coming from a file that ships with feeds and I'm having the error on a site that doesn't use "Social Parsers for Feeds" at all. I'm not sure how this can be fixed, but from what I can tell Feeds is serializing some data that shouldn't be serialized and therefore is returning errors when it attempts to unserialize. It doesn't really break anything, but makes an ugly little red error on pages that interact with the feed.

I was getting the error above on many of my cron runs and I finally figured out that what was needed was a simple check to make sure the value for $this->batch wasn't empty before attempting to unserialize:
(on line 263 of FeedsSource.inc)

if (!empty($this->batch)) {
  $this->batch = unserialize($record->batch);
}

I know that $this->batch shouldn't be empty, but obviously sometimes it is. It is probably a sign of another bug further upstream, but it seems to me that this should be altered to prevent the error if an odd value slips through.