logger(1): fix timestamps in case of long run

An example:

( echo test; sleep 2; echo test2 ) | logger -h /var/run/log

Before fix, logger assigned same timestamp to both records.

Fixes: 65547fb33db901a9f352aacb0ed45ce68b0bd275
Reported by: Vadim Goncharov
MFC after: 1 week