tlf_journal: relax stored bytes panic when block already exists (#727)
tlf_journal: relax stored bytes panic when block already exists (#727)

It's possible for the same block to be put multiple times, which
doesn't increase the stored bytes count.  This happens in particular
when a Sync fails because the disk acquire times out, and then the
Sync gets retried.

Issue: KBFS-1926
keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs