some bug for parse_item

[kcwl]

• I didn't get the right answer when i take someone test

   std::list<char> str; 
   str.push_back('\"');
   str.push_back('a');
   str.push_back('\\');
   str.push_back('\"');
   std::string test{};
   iguana::parse_item(test, str.begin(), str.end());
   CHECK(test == "a");
  

  the result of test is a\", not a

• The string to be deserialized has fewer words，maybe lesser than 7, it will crash at json_util@line 132

[qicosmos]

I think it's has been fixed, can be closed?