limit the 'recent_mailcount' to the correct time

limit the 'recent_mailcount' to the correct time

when the api call began an the end of a second, and the
database query at the beginning of the next second, while
a new mail was coming in, we would get one row to many, triggering
a result verification exception

with limiting the query to the given endtime also, we
loose at most a fraction of the second and the rowcount is
correct

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>