Fix a mistake that will return an invalid pointer

navicat-patcher/ExceptionSystem.hpp

@@ -5,13 +5,15 @@
 class SystemError : public Exception {
 private:
     const std::error_code _ErrorCode;
+    const std::string _ErrorString;
 public:
     SystemError(const char* FileName,
                 int Line,
                 unsigned long Code,
                 const char* Message) noexcept :
         Exception(FileName, Line, Message),
-        _ErrorCode(Code, std::system_category()) {}
+        _ErrorCode(Code, std::system_category()),
+        _ErrorString(_ErrorCode.message()) {}
 
     virtual bool HasErrorCode() const noexcept override {
         return true;
@@ -22,7 +24,7 @@ public:
     }
 
     virtual const char* ErrorString() const noexcept override {
-        return _ErrorCode.message().c_str();
+        return _ErrorString.c_str();
     }
 };