shell32/tests: Fix a ShellExecute() race condition.

[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=20243

Your paranoid android.


=== wvistau64 (32 bit shlexec) ===
shlexec.c:1675: Test failed: WaitForSingleObject returned 258
shlexec.c:1704: Test failed: argvA3 expected 'Open', but key not found or empty
shlexec.c:1712: Test failed: argvA4 expected 'C:\Users\winetest\AppData\Local\Temp\wtDD72.tmp\test file.noassoc.shlexec', but key not found or empty
shlexec.c:1704: Test failed: argvA3 expected 'QuotedLowerL', got 'Open'
shlexec.c:1712: Test failed: argvA4 expected 'C:\Users\winetest\AppData\Local\Temp\wtDD72.tmp\test file.shlexec', got 'C:\Users\winetest\AppData\Local\Temp\wtDD72.tmp\test file.noassoc.shlexec'
shlexec.c:1704: Test failed: argvA3 expected 'QuotedUpperL', got 'QuotedLowerL'

=== w1064 (32 bit shlexec) ===
shlexec.c:2443: Test failed: failed: rc=29 err=2
shlexec.c:2441: Test failed: ShlexecVar expected 'Present', but key not found or empty
shlexec.c:2443: Test failed: failed: rc=29 err=32
shlexec.c:2443: Test failed: failed: rc=29 err=2
shlexec.c:2441: Test failed: ShlexecVar expected 'Present', but key not found or empty
shlexec.c:2443: Test failed: failed: rc=29 err=32

=== w1064 (64 bit shlexec) ===
shlexec.c:2443: Test failed: failed: rc=29 err=2
shlexec.c:2443: Test failed: failed: rc=29 err=2
shlexec.c:2441: Test failed: ShlexecVar expected 'Present', but key not found or empty
shlexec.c:2443: Test failed: failed: rc=29 err=32
shlexec.c:2455: Test failed: ddeExec expected '[ifexec("C:\Users\winetest\AppData\Local\Temp\wt48B4.tmp\test file.sde")]', got '[open("C:\Users\winetest\AppData\Local\Temp\wt48B4.tmp\test file.sde")]'
shlexec.c:2443: Test failed: failed: rc=29 err=2
shlexec.c:2443: Test failed: failed: rc=29 err=2