proxy: fix test

Author: schzhn

Diff for: proxy/stats.go

@@ -212,10 +212,6 @@ func collectUpstreamStats(upstreams []upstream.Upstream) (stats []*UpstreamStati
 		}
 
 		dur, err := w.queryDuration, w.err
-		if dur == 0 {
-			continue
-		}
-
 		stats = append(stats, &UpstreamStatistics{
 			Error:         err,
 			Address:       w.Address(),