Fixes 'std::optional' error
--- fileshelter-5.0.1/src/fileshelter/ui/ShareDownload.hpp
+++ fileshelter-5.0.1/src/fileshelter/ui/ShareDownload.hpp
@@ -20,6 +20,7 @@
 #pragma once
 
 #include <Wt/WContainerWidget.h>
+#include <optional>
 #include "share/Types.hpp"
 
 namespace UserInterface