Posts Without Dates Are Ignored

It appears that posts that do not have dates are being skipped. I looked through the code and found that the post date was being checked against the expiration date but that there was no check to make sure a post date existed. The attached patch file adds a condition to check for the existence of the post date in the feed item before checking it against expiration date. If no post date is found the feed item is added. I don't know if anyone else would consider this the proper behavior though, it's just what I was expecting.