shell32/tests: Fix test_dde_default_app() on Windows XP SP1.

[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=20242

Your paranoid android.


=== w1064 (32 bit shlexec) ===
shlexec.c:2442: Test failed: failed: rc=29 err=2
shlexec.c:2440: Test failed: ShlexecVar expected 'Present', but key not found or empty
shlexec.c:2442: Test failed: failed: rc=29 err=32
shlexec.c:2442: Test failed: failed: rc=29 err=2
shlexec.c:2440: Test failed: ShlexecVar expected 'Present', but key not found or empty
shlexec.c:2442: Test failed: failed: rc=29 err=32

=== w1064 (64 bit shlexec) ===
shlexec.c:2442: Test failed: failed: rc=29 err=2
shlexec.c:2440: Test failed: ShlexecVar expected 'Present', but key not found or empty
shlexec.c:2442: Test failed: failed: rc=29 err=32
shlexec.c:2442: Test failed: failed: rc=29 err=2
shlexec.c:2440: Test failed: ShlexecVar expected 'Present', but key not found or empty
shlexec.c:2442: Test failed: failed: rc=29 err=32