gdi32/tests: Don't test function directly when reporting GetLastError()

[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=7979

Your paranoid android.


=== WXPPROSP3 (32 bit gdiobj) ===
TestLauncher.c:200: Test failed: Can't locate import module name in C:\winetest\gdi32_test.exe

=== W7PRO (32 bit gdiobj) ===
TestLauncher.c:200: Test failed: Can't locate import module name in C:\winetest\gdi32_test.exe

=== WVISTAADM (32 bit pen) ===
No test summary line found

=== W2K8SE (32 bit pen) ===
No test summary line found