[http3client] make sure to call `proceed_req(FINAL)` when the client supplies FIN with zero-byte of data
[http3client] make sure to call `proceed_req(FINAL)` when the client supplies FIN with zero-byte of data

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