v0.4.8

Desktop app

• Fixed a race on the relay client's roster callback. The window hands the fleet
  link the place its roster goes, and the link's read loop reads it as frames
  arrive: a window opening while the relay was already pushing a roster read and
  wrote the same field from two goroutines. It is guarded now, both where it is
  set and where it is called, so 设置 → 远程 → 应用 on a live link cannot race an
  arriving roster frame.