Fix potential hang in unit/logging_timestamp_test

If Log() fails to deliver even one newline, the fgets() later in the
test shall hang indefinitely.  So make sure we send a newline to
stderr after the Log(), to prevent that.  This shouldn't affect the
validity of the timestamp in what's sent ...
Merge pull request #1856 from ediosyncratic/timelog-fix

Fix potential hang in unit/logging_timestamp_test