cronEventAction - fix to logic

need to invert test for needReplaceOnDemandInstances and
onDemandInstance == nil

currently if onDemandInstance == nil methods return and execution stop.
This way the check to terminate a spotInstace if their number is more
than required is never done.

Assume that ASG scale down and terminate the onDemand instances that
autospotting is not terminating [autospotting_min_on_demand_number].
On the next runs onDemandInstance will be nil and spot instances in
excess will not be terminated.

core/autoscaling.go

@@ -182,18 +182,18 @@ func (a *autoScalingGroup) cronEventAction() runer {
 
 		onDemandInstance := a.getAnyUnprotectedOnDemandInstance()
 
+		if need, total := a.needReplaceOnDemandInstances(); !need {
+			logger.Printf("Not allowed to replace any more of the running OD instances in %s", a.name)
+			return terminateSpotInstance{target{asg: a, totalInstances: total}}
+		}
+
 		if onDemandInstance == nil {
 			logger.Println(a.region.name, a.name,
 				"No running unprotected on-demand instances were found, nothing to do here...")
 
 			return enableEventHandling{target{asg: a}}
 		}
 
-		if need, total := a.needReplaceOnDemandInstances(); !need {
-			logger.Printf("Not allowed to replace any more of the running OD instances in %s", a.name)
-			return terminateSpotInstance{target{asg: a, totalInstances: total}}
-		}
-
 		a.loadLaunchConfiguration()
 		return launchSpotReplacement{target{
 			onDemandInstance: onDemandInstance}}