Reuse the socks5 dialer

Fixes #644

fasthttpproxy/socks5.go

@@ -15,8 +15,13 @@ import (
 //   Dial: fasthttpproxy.FasthttpSocksDialer("localhost:9050"),
 // }
 func FasthttpSocksDialer(proxyAddr string) fasthttp.DialFunc {
+	dialer, err := proxy.SOCKS5("tcp", proxyAddr, nil, proxy.Direct)
+	// It would be nice if we could return the error here. But we can't
+	// change our API so just keep returning it in the returned Dial function.
+	// Besides the implementation of proxy.SOCKS5() at the time of writing this
+	// will always return nil as error.
+
 	return func(addr string) (net.Conn, error) {
-		dialer, err := proxy.SOCKS5("tcp", proxyAddr, nil, proxy.Direct)
 		if err != nil {
 			return nil, err
 		}