shlwapi: Fix error handling in IUnknown_GetClassID (Coverity)

[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=13825

Your paranoid android.


=== w2000pro (32 bit ordinal) ===
ordinal.c:3225: Test failed: got wrong clsid {cccccccc-cccc-cccc-cccc-cccccccccccc}

=== wxppro (32 bit ordinal) ===
ordinal.c:3225: Test failed: got wrong clsid {cccccccc-cccc-cccc-cccc-cccccccccccc}

=== w2003std (32 bit ordinal) ===
ordinal.c:3225: Test failed: got wrong clsid {cccccccc-cccc-cccc-cccc-cccccccccccc}