adjust state_unloading_cycle compuation order in nmethod::is_unloading

Move state_unloading_cycle computation after state_is_unloading checking in nmethod::is_unloading(). Avoiding useless state_unloading_cycle computation when state_is_unloading is true.

  uint8_t state = RawAccess<MO_RELAXED>::load(&_is_unloading_state);
  bool state_is_unloading = IsUnloadingState::is_unloading(state);
  uint8_t state_unloading_cycle = IsUnloadingState::unloading_cycle(state); // compute early, useless if stat_is_unloading is true.
  if (state_is_unloading) {
    return true;
  }
  uint8_t current_cycle = CodeCache::unloading_cycle();
  if (state_unloading_cycle == current_cycle) {
    return false;
  }