fix digest preview not working on mysql because of a quoted LIMIT argument

classes/digest.php

@@ -132,8 +132,8 @@ class Digest
 				AND unread = true
 				AND score >= 0
 			ORDER BY ttrss_feed_categories.title, ttrss_feeds.title, score DESC, date_updated DESC
-			LIMIT :limit");
-		$sth->execute([':user_id' => $user_id, ':limit' => $limit]);
+			LIMIT " . (int)$limit);
+		$sth->execute([':user_id' => $user_id]);
 
 		$headlines_count = 0;
 		$headlines = array();