common/LogClient: fix sending dup log items

We need to skip even the most recently sent item in order to get to the
ones we haven't sent yet.

Fixes: #9080
Backport: firefly, dumpling
Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit 057c6808be5bc61c3f1ac2b956c1522f18411245)