HttpAsyncService.exception(...) should shutdown connection on IOException

Currently, HttpAsyncService.exception(...) closes connection if response is already submitted. On TCP RST packet received all futher attempts to write into socket will result in IOException, but SelectionKey.readyOps() won't be changed. So, if connection output buffer has some unsent data, BaseIOReactor.writable() will be called again and again, but no data will be written, so reactor thread will stuck.

I suggest to shutdown connection if IOException occured, this will save from infinite calls to BaseIOReactor.writable()