BUG/MINOR: h1: reject CONNECT authorities with an empty host

BUG/MINOR: h1: reject CONNECT authorities with an empty host

h1_validate_connect_authority() checks that the authority of a CONNECT
request contains a non-empty port, but it doesn't check the host part. So
"CONNECT :443 HTTP/1.1" was accepted and forwarded with or without a Host
header, and with "Host: :443" the Host header was even normalized to an
empty value. Such a target is invalid (RFC9112#3.2.3 requires a
uri-host). Let's reject it.

This was introduced by commit 3f5fbe940 ("BUG/MEDIUM: h1: Improve authority
validation for CONNCET request") in 2.7. It should be backported as far as
2.8.