ole32/tests: Fix crashes in PropVariantClear tests under win2000 and XP.

[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
https://testbot.winehq.org/JobDetails.pl?Key=6384

Your paranoid android.


=== w2008s64 (64 bit propvariant) ===
propvariant: unhandled exception c0000005 at 000007FEFF6093CE