wintrust/tests: Fix a leak (valgrind)

[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=9309

Your paranoid android.


=== W2K8SE (32 bit softpub) ===
softpub.c:742: Test failed: expected TRUST_E_NOSIGNATURE or CRYPT_E_FILE_ERROR, got 80092003