oledb32: Implement GetConversionSize DBTYPE_STR->DBTYPE_WSTR

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
http://testbot.winehq.org/JobDetails.pl?Key=25234

Your paranoid android.


=== W2KPROSP4 (32 bit convert) ===
convert.c:2537: Test failed: 12