http: Fix authentication, broken since 6a463e7f

The cur_*auth_type variables were set before the http_connect call
prior to 6a463e7f - their sole purpose is to record the
authentication type used to do the latest request, since parsing
the http response sets the new type in the auth state.

CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>