charterm event not ready when bytes are available

[b2coutts]

While attempting to sync on the charterm event with a timeout, by mashing keys very quickly, it is possible to put charterm in a state where the charterm event is not ready for synchronization, and yet (charterm-byte-ready?) produces #t. Strangely, this only occurs when (charterm-screen-size) is called after sync/timeout.

Attached is a small program that causes this behaviour; it can be induced by simply mashing keys as fast as possible. See the comment at the beginning of the program.