Raise ArgumentError with empty host url again.

  Fixup ruby/ruby@dd5118f

ruby/ruby@1cda414

Co-authored-by: Koichi Sasada <ko1@atdot.net>

lib/net/http/generic_request.rb

@@ -15,7 +15,8 @@ def initialize(m, reqbody, resbody, uri_or_path, initheader = nil)
 
     if URI === uri_or_path then
       raise ArgumentError, "not an HTTP URI" unless URI::HTTP === uri_or_path
-      raise ArgumentError, "no host component for URI" unless uri_or_path.hostname
+      hostname = uri_or_path.hostname
+      raise ArgumentError, "no host component for URI" unless (hostname && hostname.length > 0)
       @uri = uri_or_path.dup
       host = @uri.hostname.dup
       host << ":".freeze << @uri.port.to_s if @uri.port != @uri.default_port