We currently have a chickend-and-egg situation in some environments
where we can set up routes that WinHTTP's WPAD/PAC resolution service
needs to download the PAC file to evaluate GetProxyForURL, but the PAC
file is behind a route for which we need to call GetProxyForURL to
e.g. dial a DERP server.
As a short-term fix, just assume that the most recently returned proxy
is good enough for such situations.
