BUG: parsed string length not correctly considered

[bpintea]

The library does not correctly consider the length when parsing the input string. If the string is not a NTS, the library will read past the indicated limit.

If the library is passed a correctly formatted JSON and the character next to the indicated end is a non-white space character, the parsing will succeed. But:

• if the JSON is incorrect, the parsing can crash;
• if the end+1 character is a white string, the parsing will incorrectly fail (for a correct JSON string).