net/http: fix panic when status without description for proxied HTTPS responses

net/http: fix panic when status without description for proxied HTTPS responses

Check to ensure that Status is set
when parsing a proxied HTTPS response
that a CONNECT proxy-authorization.

Fixes #21701

Change-Id: Id91700b83425420101e0b0d46e12aaf5d20fd3a3
Reviewed-on: https://go-review.googlesource.com/59990
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Tom Bergan <tombergan@google.com>