In fetch_resolve(), if the port number or service name is included in
the host argument (e.g. "www.freebsd.org:443"), the service pointer,
which is supposed to point to the port or service part, instead points
to the separator, causing getaddrinfo() to fail.

Note that I have not been able to trigger this bug with fetch(1), nor
do I believe it is possible, as libfetch always parses the host:port
specification itself. I discovered it when I copied fetch_resolve()
into an unrelated project.

MFC after: 3 days