In RFC3986#6.2.3, following URIs are considered as equivalent:
http://example.comhttp://example.com/http://example.com:/http://example.com:80/
The third one is interristing because the port is empty and it is still
considered as a default port. Thus, http_get_host_port() does no longer
return IST_NULL when the port is empty. Now, a ist is returned, it points on
the first character after the colon (':') with a length of 0. In addition,
http_is_default_port() now considers an empty port as a default port,
regardless the scheme.
This patch must not be backported, if so, without the previous one ("MINOR:
h1: Consider empty port as invalid in authority for CONNECT").
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