Fix nil panic when config has no spec.k0s (#291)

Signed-off-by: Kimmo Lehto <[email protected]>

Author: kke

pkg/apis/k0sctl.k0sproject.io/v1beta1/cluster/spec.go

@@ -19,6 +19,7 @@ type Spec struct {
 func (s *Spec) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	type spec Spec
 	ys := (*spec)(s)
+	ys.K0s = &K0s{}
 
 	if err := unmarshal(ys); err != nil {
 		return err