Partial workaround for meter during a clock jump

Author: vincentbernat

meter.go

@@ -190,10 +190,13 @@ func (m *StandardMeter) Snapshot() Meter {
 func (m *StandardMeter) updateSnapshot() {
 	// should run with write lock held on m.lock
 	snapshot := m.snapshot
-	snapshot.rate1 = m.a1.Rate()
-	snapshot.rate5 = m.a5.Rate()
-	snapshot.rate15 = m.a15.Rate()
-	snapshot.rateMean = float64(snapshot.count) / time.Since(m.startTime).Seconds()
+	elapsed := time.Since(m.startTime).Seconds()
+	if elapsed >= 0 {
+		snapshot.rate1 = m.a1.Rate()
+		snapshot.rate5 = m.a5.Rate()
+		snapshot.rate15 = m.a15.Rate()
+		snapshot.rateMean = float64(snapshot.count) / elapsed
+	}
 }
 
 func (m *StandardMeter) tick() {