journal: possible race condition between flush and append callback

journal: possible race condition between flush and append callback

When notifying the journal recorder of an overflow or if the object
close request has completed due to no more in-flight IO, it was
possible for a race between a flush request and the processing of
an append completion to attempt to kick off duplicate notifications.
Since the overflowed and closed callbacks are properly protected from
duplicates, use a counter instead of a boolean to track possible
in-flight handler callbacks.

Fixes: https://tracker.ceph.com/issues/47880
Signed-off-by: Jason Dillaman <dillaman@redhat.com>