fix utf8 support

src/util/stringutil.hpp

@@ -11,7 +11,7 @@ namespace util {
     std::string escape(std::string_view s, bool escapeUnicode=true);
 
     /// @brief Escape all special XML characters 
-    std::string escape_xml(std::string_view s);
+    std::wstring escape_xml(std::wstring_view s);
 
     /// @brief Function used for error messages
     std::string quote(const std::string& s);