fix simult close
fix simult close

keep local of callbacks.on_sent

OptimusLime/lua-websockets,OptimusLime/lua-websockets,enginix/lua-websockets,lipp/lua-websockets,enginix/lua-websockets,OptimusLime/lua-websockets,KSDaemon/lua-websockets,lipp/lua-websockets,enginix/lua-websockets,KSDaemon/lua-websockets,KSDaemon/lua-websockets,lipp/lua-websockets