Merge "Validate periodic_sync before use in SyncLost to fix crash" into main

    LOG_DEBUG("[PSync]: sync_handle = %d", sync_handle);

    callbacks_->OnPeriodicSyncLost(sync_handle);

    auto periodic_sync = GetEstablishedSyncFromHandle(sync_handle);

    if (periodic_sync == periodic_syncs_.end()) {

      LOG_ERROR("[PSync]: index not found for handle %u", sync_handle);

      return;

    }

    periodic_syncs_.erase(periodic_sync);

  }