http_proxy: a compilation error was fixed

[majstar]

Hello.
I faced a compilation error when was building cURL with CURL_DOES_CONVERSIONS defined. The problem occurred because some variables in curl/lib/http_proxy.c were moved to the structure http_connect_state in 5113ad0.
The issue is present only when CURL_DOES_CONVERSIONS defined because, otherwise, calls of Curl_convert_from_network are removed from the code at the preprocessing stage.

[coveralls]

Coverage decreased (-0.04%) to 73.162% when pulling fd80201 on majstar:master into ca9630f on curl:master.

[jay]

Thanks