get_article_tags: while getting tags from cache check if article entry actually exists

include/functions2.php

@@ -1121,6 +1121,7 @@
 			$result = db_query("SELECT tag_cache FROM ttrss_user_entries
 				WHERE ref_id = '$id' AND owner_uid = $owner_uid");
 
+			if (db_num_rows($result) != 0)
 				$tag_cache = db_fetch_result($result, 0, "tag_cache");
 		}