fix issue: The web_proxy doesn't work when set proxy with uri #1780
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http_client_winhttp::send_request only handle the case when proxy.is_auto_discovery() return true.


So when we construct a web_proxy with uri, it will only set the proxy mode as user_provided_.
So send_request will ignore the proxy setting when we use uri to construct a web_proxy.
My modification tries to fix the problem.