(unlock_display): If adding to kbd_queue, set kbd_queue_has_data.

(unlock_display): If adding to kbd_queue, set kbd_queue_has_data.
(read_char): Set and clear kbd_queue_has_data appropriately, but
leave it unset when we push back an incomplete sequence.
(read_char): Take the longjmp even if current_perdisplay was null.
(readable_events): Check kbd_queue_has_data instead of kbd_queue.
(init_perdisplay): Initialize kbd_queue_has_data.