Crash with ClusterStack Resource with empty `providerRef` and `noProvider`

Reproduce the crash with the ClusterStack spec in the issue, then start at internal/controller/clusterstack_controller.go:275 and trace back through Reconcile at line 178. Check the missing providerRef/noProvider error path and determine why handling or printing the error dereferences nil. Done means the same resource produces an error without panicking.

The CSO crashes with the following ClusterStack spec

apiVersion: clusterstack.x-k8s.io/v1alpha1                                                                             
kind: ClusterStack
metadata:
  name: scs-cluster-stack
  namespace: default
spec:
  provider: openstack
  name: scs
  kubernetesVersion: "1.27"
  channel: stable
  autoSubscribe: false
  versions:
    - v4

I think the missing providerRef is actually detected and the crash happens when printing the Error message, however i have not investigated deeply. The crashlog is:

{"level":"INFO","time":"2024-05-22T09:15:41.002Z","file":"controller/controller.go:115","message":"Observed a panic in reconciler: runtime error: invalid memory address or nil pointer dereference","controller":"clusterstack","controllerGroup":"clusterstack.x-k8s.io","controllerKind":"ClusterStack","ClusterStack":{"name":"scs-cluster-stack","namespace":"default"},"namespace":"default","name":"scs-cluster-stack","reconcileID":"66ffaad8-291e-43a7-aa54-d5ba5f5ce8f3"}
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x19082d4]

goroutine 204 [running]:
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile.func1()
	/src/cluster-stack-operator/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:116 +0x1e5
panic({0x1b76920?, 0x313ed60?})
	/usr/local/go/src/runtime/panic.go:914 +0x21f
github.com/SovereignCloudStack/cluster-stack-operator/internal/controller.(*ClusterStackReconciler).createOrUpdateProviderClusterStackRelease(0xc00028fc00, {0x213be10, 0xc0006915c0}, {0xc0005a29f0, 0x15}, 0xc0003d2380)
	/src/cluster-stack-operator/internal/controller/clusterstack_controller.go:275 +0xf4
github.com/SovereignCloudStack/cluster-stack-operator/internal/controller.(*ClusterStackReconciler).Reconcile(0xc00028fc00, {0x213be10?, 0xc0006915c0}, {{{0xc0002e0796?, 0x5?}, {0xc0002440d8?, 0xc0004a1d48?}}})
	/src/cluster-stack-operator/internal/controller/clusterstack_controller.go:178 +0x1073
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile(0x213f928?, {0x213be10?, 0xc0006915c0?}, {{{0xc0002e0796?, 0xb?}, {0xc0002440d8?, 0x0?}}})
	/src/cluster-stack-operator/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:119 +0xb7
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler(0xc0004b4c80, {0x213be48, 0xc0003a6f00}, {0x1c5ec60?, 0xc0002230c0?})
	/src/cluster-stack-operator/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:316 +0x3cc
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem(0xc0004b4c80, {0x213be48, 0xc0003a6f00})
	/src/cluster-stack-operator/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:266 +0x1c9
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2()
	/src/cluster-stack-operator/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:227 +0x79
created by sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2 in goroutine 92
	/src/cluster-stack-operator/vendor/sigs.k8s.io/controller-runtime/pkg/internal/controller/controller.go:223 +0x565