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

[Hans Leidekker]

On Thu, 2012-11-01 at 14:52 +0100, Marvin wrote:
> 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

This is a timeout unrelated to the tests I added. Here's a job running
new tests only: https://testbot.winehq.org/JobDetails.pl?Key=22629