fix merr logic.
fix merr logic.

Signed-off-by: Krasi Georgiev <92e9bca555ae3f6bf713b708c97f3f6dcff65542@redhat.com>

GoogleCloudPlatform/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,keegancsmith/prometheus,alileza/prometheus,kangwoo/prometheus,keegancsmith/prometheus,Gouthamve/prometheus,Gouthamve/prometheus,prometheus/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,kangwoo/prometheus,alileza/prometheus,prometheus/tsdb,Gouthamve/prometheus,alileza/prometheus,prometheus/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,alileza/prometheus,Gouthamve/prometheus