ddraw/tests: Better clean up when skipping the primary palette tests.

[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://newtestbot.winehq.org/JobDetails.pl?Key=4972

Your paranoid android.


=== w8 (32 bit ddraw2) ===
ddraw2.c:3231: Test failed: SetDisplayMode failed, hr 0x80004001.

=== w8 (32 bit ddraw4) ===
ddraw4.c:3462: Test failed: SetDisplayMode failed, hr 0x80004001.