fix: nil pointer in checkDiffAndPrepareUpdate for MasterAuthorizedNetworksConfig

Initialize DesiredControlPlaneEndpointsConfig and IpEndpointsConfig
before assigning AuthorizedNetworksConfig to prevent nil pointer
dereference during cluster reconciliation.

When reconciling a GKE cluster, checkDiffAndPrepareUpdate compares the
desired MasterAuthorizedNetworksConfig with the existing one. If they
differ, it attempts to set clusterUpdate.DesiredControlPlaneEndpointsConfig
.IpEndpointsConfig.AuthorizedNetworksConfig without first initializing
the parent structs, causing a nil pointer dereference.

This is related to issue #1497 but affects the update/reconciliation
path rather than the creation path addressed in PR #1503.

Signed-off-by: Piotr Kieszczyński <piotr.kieszczynski@gmail.com>

Author: pkieszcz

cloud/services/container/clusters/reconcile.go

@@ -516,6 +516,12 @@ func (s *Service) checkDiffAndPrepareUpdate(existingCluster *containerpb.Cluster
 	desiredMasterAuthorizedNetworksConfig := convertToSdkMasterAuthorizedNetworksConfig(s.scope.GCPManagedControlPlane.Spec.MasterAuthorizedNetworksConfig)
 	if !compareMasterAuthorizedNetworksConfig(desiredMasterAuthorizedNetworksConfig, existingCluster.GetControlPlaneEndpointsConfig().GetIpEndpointsConfig().GetAuthorizedNetworksConfig()) {
 		needUpdate = true
+		if clusterUpdate.DesiredControlPlaneEndpointsConfig == nil {
+			clusterUpdate.DesiredControlPlaneEndpointsConfig = &containerpb.ControlPlaneEndpointsConfig{}
+		}
+		if clusterUpdate.DesiredControlPlaneEndpointsConfig.IpEndpointsConfig == nil {
+			clusterUpdate.DesiredControlPlaneEndpointsConfig.IpEndpointsConfig = &containerpb.ControlPlaneEndpointsConfig_IPEndpointsConfig{}
+		}
 		clusterUpdate.DesiredControlPlaneEndpointsConfig.IpEndpointsConfig.AuthorizedNetworksConfig = desiredMasterAuthorizedNetworksConfig
 		log.V(2).Info("Master authorized networks config update required", "current", existingCluster.GetControlPlaneEndpointsConfig().GetIpEndpointsConfig().GetAuthorizedNetworksConfig(), "desired", desiredMasterAuthorizedNetworksConfig)
 	}