do not assume constant year based on file index

do not assume constant year based on file index

rather start with the current time at invocation and if the month in
the log is larger assume a year-wrap happened between logwriting and
invocation.

the old logic is flawed (but that can be said about parsing
traditional syslog timestamps (w/o year) in general) - it got worse
with the change in bullseye of rotating syslog weekly by default -
resulting in users losing one week of logs per day in the new year as
reported in https://forum.proxmox.com/threads/.102322/

Reviewed-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>