some very minor php8.1 warnings fixed

Author: Andrew Dolgov

classes/feeds.php

@@ -122,7 +122,7 @@ private function _format_headlines_list($feed, string $method, string $view_mode
 		$feed_title = $qfh_ret[1];
 		$feed_site_url = $qfh_ret[2];
 		$last_error = $qfh_ret[3];
-		$last_updated = strpos($qfh_ret[4], '1970-') === false ?
+		$last_updated = strpos($qfh_ret[4] ?? "", '1970-') === false ?
 			TimeHelper::make_local_datetime($qfh_ret[4], false) : __("Never");
 		$highlight_words = $qfh_ret[5];
 		$reply['first_id'] = $qfh_ret[6];

classes/rssutils.php

@@ -447,7 +447,7 @@ function ($result, $plugin) use (&$feed_data, $start_ts) {
 				Debug::log("not using CURL due to open_basedir restrictions", Debug::LOG_VERBOSE);
 			}
 
-			if (time() - strtotime($feed_obj->last_unconditional) > Config::get(Config::MAX_CONDITIONAL_INTERVAL)) {
+			if (time() - strtotime($feed_obj->last_unconditional ?? "") > Config::get(Config::MAX_CONDITIONAL_INTERVAL)) {
 				Debug::log("maximum allowed interval for conditional requests exceeded, forcing refetch", Debug::LOG_VERBOSE);
 
 				$force_refetch = true;