Sets app status to unknown if there is an error. Closes #2577 (#2578)

controller/state.go

@@ -412,6 +412,10 @@ func (m *appStateManager) CompareAppState(app *v1alpha1.Application, revision st
 		} else {
 			resState.Status = v1alpha1.SyncStatusCodeSynced
 		}
+		// we can't say anything about the status if we were unable to get the target objects
+		if failedToLoadObjs {
+			resState.Status = v1alpha1.SyncStatusCodeUnknown
+		}
 		managedResources[i] = managedResource{
 			Name:      resState.Name,
 			Namespace: resState.Namespace,