handle zero-length `host` header field the same way as the header is missing
handle zero-length `host` header field the same way as the header is missing

h2o/h2o,devnexen/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,yannick/h2o,h2o/h2o,devnexen/h2o,devnexen/h2o,devnexen/h2o,devnexen/h2o,devnexen/h2o,h2o/h2o,h2o/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,h2o/h2o,h2o/h2o,yannick/h2o,yannick/h2o,h2o/h2o,devnexen/h2o,h2o/h2o,yannick/h2o,yannick/h2o,h2o/h2o