check_feed_favicon: only guess favicon url when local icon doesn't exist (closes #369)

functions.php

@@ -465,14 +465,16 @@
 	} // function get_favicon_url
 
 	function check_feed_favicon($site_url, $feed, $link) {
-		$favicon_url = get_favicon_url($site_url);
-
 #		print "FAVICON [$site_url]: $favicon_url\n";
 
 		$icon_file = ICONS_DIR . "/$feed.ico";
 
-		if ($favicon_url && !file_exists($icon_file)) {
+		if (!file_exists($icon_file)) {
+			$favicon_url = get_favicon_url($site_url);
+
+			if ($favicon_url) {
 				$contents = fetch_file_contents($favicon_url, "image");
+
 				if ($contents) {
 					$fp = fopen($icon_file, "w");
 
@@ -484,6 +486,7 @@
 				}
 			}
 		}
+	}
 
 	function update_rss_feed($link, $feed, $ignore_daemon = false, $no_cache = false) {