Panic with devision by 0 if all pods are ignored

[tony-bondarenko]

If all pods are ignored there is division by 0 panic in replica calculation process.

watermarkpodautoscaler/controllers/datadoghq/replica_calculator.go

Line 223 in c524600

ratioReadyPods := int32(100 * readyPodCount / (len(podList) - len(ignoredPods)))