cluster shell default command breaks after a cluster delete

[pepov]

Describe the bug
I create a cluster, then use cluster shell to interact with it. When I delete the cluster the default banzai cluster shell command no longer works, just if I set --cluster or --cluster-name explicitly.

Expected behavior
The default cluster shell command should work even if the previously used cluster is deleted.

Additional info
My best guess is that the previous cluster's env vars are still set while the context.Init function assumes that the cluster still exists:
https://github.com/banzaicloud/banzai-cli/blob/master/internal/cli/command/cluster/context/context.go#L77