Fix #35795: A time consumed could be -1

Fix #35795: A time consumed could be -1

* [shogi-server] shogi_server/time_clock.rb:
  - A time consumed could be -1.
    * The start time of a move is captured after sending a move to a
      player of the next turn at the end of the giant lock
    * The end time of the move is captured at the exact time when the
      server receives it before the giant lock
    Therefore, end_time < start_time is possible when a player returns a
    move instantly.
    Thanks to Tomoyuki Kaneko for reporting this issue.
    (Closes: #35795)