detach download contexts and unref when canceling them
detach download contexts and unref when canceling them

syndicate-storage/syndicate-core,iychoi/syndicate-core,iychoi/syndicate-core,iychoi/syndicate-core,syndicate-storage/syndicate-core,syndicate-storage/syndicate-core,syndicate-storage/syndicate-core,iychoi/syndicate-core