Fix invalid last update timestamp

inc/feed.php

@@ -45,7 +45,7 @@ class Feed extends PhpObject {
 		$this->iFeedId = $iFeedId;
 		$asFeed = $this->getFeed();
 		$this->sRefFeedId = $asFeed['ref_feed_id'];
-		$this->iLastUpdate = strtotime($asFeed['last_update']);
+		$this->iLastUpdate = $asFeed['last_update']=='0000-00-00 00:00:00'?0:strtotime($asFeed['last_update']);
 	}
 
 	public function createFeedId($oProjectId) {