folder_block_ops: clean up deferred byte count on unrecoverable error
folder_block_ops: clean up deferred byte count on unrecoverable error

Issue: KBFS-1508

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/client,keybase/client