ObjFW  View Ticket

Currently, `OFString` does not reject a `\0` within the string. However, `OFString`s often get passed as C strings. Therefore, either one of the following should be done:

 * Audit all occurrences where an `OFString` is passed as a C string.
 * Truncate the length to the first occurrence of `\0`.
 * Extend the current string checking code to reject `\0` in there if a length has been specified.
   * If no length has been specified, it cannot be longer until the `\0` anyway.
   * A good place for this would be in the code that checks whether the passed string is valid UTF-8, to avoid going through the same string twice.
     * This means strings of another encoding need to check for `\0` during their conversion to UTF-8, as UTF-8 is not validated there since it was just converted and hence assumed correct.

The first option probably doesn't scale, as there are many places where an `OFString` is passed as a C string and doesn't cover where this is being done outside of ObjFW. So this would be a potential foot gun for users.

The second option might be unexpected and lead to bugs, because the user has just specified a length for the string to create, but the just created string has a different length.

Therefore, the third option probably makes most sense.

Another option is to allow \0 in strings, but throw an `OFInvalidEncodingException` for any method that returns a \0 terminated string. This is probably the best option.

Implemented in [](6fbc3b18c7).

Further tests will be added later, but for now, this is tested via the JSON tests.