[release-1.13] Reset the Spec.InitialRevisions for RolloutOrchestrator the when route traffic is empty (#156)

* [release-1.13] Reset the Spec.InitialRevisions for RolloutOrchestrator the when route traffic is empty

* Added the test cases

Author: houshengbo

pkg/reconciler/service/resources/rolloutorchestrator.go

@@ -228,6 +228,8 @@ func NewInitialFinalTargetRev(initialRevisionStatus, ultimateRevisionTarget []v1
 }
 
 // UpdateInitialFinalTargetRev updates InitialRevisions, TargetRevisions and StageTargetRevisions for RolloutOrchestrator.
+// Param: ultimateRevisionTarget is the most updated target revisions.
+// Param: ro is the custom resource of RolloutOrchestrator.
 func UpdateInitialFinalTargetRev(ultimateRevisionTarget []v1.TargetRevision, ro *v1.RolloutOrchestrator,
 	route *servingv1.Route, deploymentLister appsv1listers.DeploymentLister) {
 	if !trafficEqual(ro.Spec.TargetRevisions, ultimateRevisionTarget) {
@@ -267,7 +269,8 @@ func UpdateInitialFinalTargetRev(ultimateRevisionTarget []v1.TargetRevision, ro
 					}
 				}
 			}
-		} else {
+		} else if route == nil || len(route.Status.Traffic) == 0 {
+			// If route.Status.Traffic is empty, no revision is assigned to any traffic, and reset the InitialRevisions.
 			// Reset the InitialRevisions, if StageRevisionStatus in the status is empty.
 			ro.Spec.InitialRevisions = nil
 		}