Proxy-Authorization was added only when both the proxy username and the
proxy password were set, and a cross-host redirect carried the proxy
credentials over only when the username was set. Authorization has been
sent when either one is set since #958; do the same for the proxy.
A client that has both a proxy Basic credential with one empty field
and a proxy bearer token now sends Basic rather than Bearer, the order
Authorization already follows.
yhirose
941745c33d
