dat.pl: do not die on measured performance values or errors equal to 0
dat.pl: do not die on measured performance values or errors equal to 0

It is actually possible and valid for these to be 0 -- especially
the error.

Signed-off-by: Emilio G. Cota <201e881bfa0e9543bba00630d033ebfb953e7c40@braap.org>

cota/dbt-bench