curl: free the user-provided proxy credentials

Author: carlosmn

src/curl_stream.c

@@ -297,6 +297,7 @@ static void curls_free(git_stream *stream)
 	curls_close(stream);
 	git_strarray_free(&s->cert_info_strings);
 	git_proxy_options_free(&s->proxy);
+	git_cred_free(s->proxy_cred);
 	git__free(s);
 }