22106 FIX job: report the outcome of a run whose start time is missing

Werk 22105 made a completed run without a readable start time report UNKNOWN
instead of crashing - and nothing else, although the exit code and the metrics
of that run were sitting in the file. The exit code does not depend on the start
time, so a job that had failed showed up as UNKNOWN rather than CRIT - and on a
host running a 2.4 agent without perl that is every failing job, which is the
very situation werk 22105 was written for.

The outcome and the metrics of such a run are now reported as usual, and only
the job age is missing. A failed run reaches CRIT again; a successful one is
still UNKNOWN, because the missing job age is still reported as such.

The start time drops out of the guard, and the else branch at the end of
check_job - dead until now, and commented as such - becomes where the missing
start time is reported. It is reachable exactly when there is a completed job
without a start time and nothing running, which is what used to take the guard.

CMK-35333

Change-Id: If751fdc3954e17f240313b24759c4ad68a983663