Fix behaviour when favicon url is not found

If url is not find, we copy default favicon into favicon dir so at the next
try, we don't search the url again.

See https://github.com/FreshRSS/FreshRSS/issues/290
See https://github.com/FreshRSS/FreshRSS/issues/727

p/f.php

@@ -7,19 +7,19 @@ include(LIB_PATH . '/Favicon/DataAccess.php');
 
 
 $favicons_dir = DATA_PATH . '/favicons/';
-$default_favicon = PUBLIC_PATH . '/themes/icons/default_favicon.png';
+$default_favicon = PUBLIC_PATH . '/themes/icons/default_favicon.ico';
 
 
 /* Télécharge le favicon d'un site et le place sur le serveur */
 function download_favicon($website, $dest) {
-	global $favicons_dir;
+	global $favicons_dir, $default_favicon;
 
 	$favicon_getter = new \Favicon\Favicon();
 	$favicon_getter->setCacheDir($favicons_dir);
 	$favicon_url = $favicon_getter->get($website);
 
 	if ($favicon_url === false) {
-		return false;
+		return @copy($default_favicon, $dest);
 	}
 
 	$c = curl_init($favicon_url);
@@ -47,7 +47,7 @@ function show_default_favicon() {
 	global $default_favicon;
 
 	header('HTTP/1.1 404 Not Found');
-	header('Content-Type: image/png');
+	header('Content-Type: image/ico');
 	readfile($default_favicon);
 	die();
 }