Cygwin: console: Fix typeahead key swapping which still occurs.

Cygwin: console: Fix typeahead key swapping which still occurs.

- The commit "Cygwin: console: Improve the code to avoid typeahead
  key swapping." did not solve the problem enough. Two unexpected
  things happen.
  (1) wVirtualKeyCode and wVirtualScanCode of readback key event may
      be null'ed even if they are not zero on WriteConsoleInputW().
      Therefore, memcmp() may report the event sequence is not equal.
  (2) WriteConsoleInputW() may not be atomic. The event sequence
      which is written by WriteConsoleInputW() may be inserted by
      key input in the middle of the sequence. Current code gives
      up to fix in this situation.
  This patch should fix that issue.