Silence PHP notices in upstream Parsedown

Parsedown is a still unresolved issue in whole, this at least ensures that we don't fill up logfiles with useless errors...

lib/Pico.php

@@ -1673,7 +1673,7 @@ public function substituteFileContent($markdown, array $meta = array())
     public function parseFileContent($markdown, $singleLine = false)
     {
         $markdownParser = $this->getParsedown();
-        return !$singleLine ? $markdownParser->text($markdown) : $markdownParser->line($markdown);
+        return !$singleLine ? @$markdownParser->text($markdown) : @$markdownParser->line($markdown);
     }
 
     /**