Investigate lingering file waiter in bad `ttysize`

[klange]

Prior to 0780718, ttysize was incorrectly using the (buffered) stdio interfaces to read characters after an fswait2 call on stdin, which resulted in a single character being read from the buffer and the next call to fswait2 blocking until it times out. When additional input was received on the tty, after the timeout had expired and ttysize exited, the stale ttysize process was still in the alert list for the tty, resulting in an attempt to awaken an invalid process.

Investigate why the stale process was still in the alert queue despite the timeout expiring and the process exiting.