In the XML standard, entities must start with 'x' if they are hex

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@9515 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/utils/string_utils.cpp

@@ -581,7 +581,7 @@ namespace StringUtils
                 }
                 else
                 {
-                    output <<"&#" << std::hex <<std::uppercase<< s[i]<<";";
+                    output <<"&#x" << std::hex <<std::uppercase<< s[i]<<";";
                 }
             }
         }