[PATCH] mfplat/tests: Avoid cast from COM object to interface

[Marvin]

Hi,

While running your changed tests, 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=96349

Your paranoid android.


=== debiant2 (32 bit report) ===

mfplat:
mfplat.c:3753: Test failed: Unexpected refcount 1.
Unhandled exception: page fault on execute access to 0x00000000 in 32-bit code (0x00000000).