The charset conversion uses different error reporting in ICONV and Windows API

[Paolo Brandoli]

When a conversion from/to unicode in Windows fails, then an empty string is returned, while with ICONV an exception is thrown.

This causes different behaviours when the library is compiled in linux or windows.

The windows solution has to be preferred, since dataHandlerStringUnicode relies on that

[Paolo Brandoli]

- Fixes #52 (The charset conversion uses different error reporting in ICONV and Windows API)

→ a2cfec2af6dd