Handle possible invalid iterator issue during settings parsing

components/config/gamesettings.cpp

@@ -338,6 +338,9 @@ bool Config::GameSettings::writeFileWithComments(QFile &file)
             if (!comments.empty() && index != -1 && settingRegex.captureCount() >= 2 &&
                 mUserSettings.find(settingRegex.cap(1)) != mUserSettings.end())
             {
+                if (commentStart == fileCopy.end())
+                    throw std::runtime_error("Config::GameSettings: failed to parse settings - iterator is past of end of settings file");
+
                 for (std::vector<QString>::const_iterator it = comments.begin(); it != comments.end(); ++it)
                 {
                     *commentStart = *it;