comdlg32/tests: make sure to use a return value (LLVM/Clang)

[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=12798

Your paranoid android.


=== W7PROX64 (32 bit itemdlg) ===
itemdlg: unhandled exception c0000005 at 75B94C19