folder_branch_ops: fix missing block change swaps
folder_branch_ops: fix missing block change swaps

Without this, the block archiver won't see blocks to unreference in CR
resolutions if the block changes are unembedded.

Issue: KBFS-1338

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