[2/3] ole32/tests: Add more tests for PropVariantClear.

[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=6359

Your paranoid android.


=== w2000pro (32 bit propvariant) ===
propvariant: unhandled exception c0000005 at 779DB8A8

=== w8 (32 bit propvariant) ===
propvariant: unhandled exception c0000005 at 7527DF57