winhttp: Fix the error returned from WinHttpGetProxyForUrl when autodetection fails.

[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=22654

Your paranoid android.


=== WXPPROSP3 (32 bit winhttp) ===
winhttp.c:2405: Test failed: got 80072ee2
winhttp.c:2411: Test failed: got 8000000a