Check for fileinfo

https://github.com/FreshRSS/FreshRSS/issues/1402
https://github.com/FreshRSS/FreshRSS/issues/1461

lib/Favicon/Favicon.php

@@ -179,7 +179,7 @@ class Favicon
         // Sometimes people lie, so check the status.
         // And sometimes, it's not even an image. Sneaky bastards!
         // If cacheDir isn't writable, that's not our problem
-        if ($favicon && is_writable($this->cacheDir) && !$this->checkImageMType($favicon)) {
+        if ($favicon && is_writable($this->cacheDir) && extension_loaded('fileinfo') && !$this->checkImageMType($favicon)) {
             $favicon = false;
         }