read16bitstring() is buggy in v2.21

```
Function read16bitstring() incorrectly calculates length of 16-bit strings,
resulting in cropped strings and
corresponding notices from iconv() about incomplete multibyte characters.

To fix, please replace (line 830):

while (ord($data[$start + $len]) + ord($data[$start + $len + 1]) > 0) $len++;

with:

while (ord($data[$start + $len]) + ord($data[$start + $len + 1]) > 0) $len+=2;
```

Original issue reported on code.google.com by `alexanderk23` on 22 Apr 2010 at 7:45

Start in the read16bitstring() function at line 830 and inspect how $len advances while scanning $data. Apply the requested length-step correction, then verify that 16-bit strings are no longer cropped and that iconv() no longer reports incomplete multibyte characters.

Written by the indexing model from the issue text.