fix issue preveting get node when disco is missing (#1919)

Fixed #1816

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/types/node.go

@@ -306,11 +306,15 @@ func (node *Node) AfterFind(tx *gorm.DB) error {
 	}
 	node.NodeKey = nodeKey
 
+	// DiscoKey might be empty if a node has not sent it to headscale.
+	// This means that this might fail if the disco key is empty.
+	if node.DiscoKeyDatabaseField != "" {
 		var discoKey key.DiscoPublic
 		if err := discoKey.UnmarshalText([]byte(node.DiscoKeyDatabaseField)); err != nil {
 			return fmt.Errorf("unmarshalling disco key from db: %w", err)
 		}
 		node.DiscoKey = discoKey
+	}
 
 	endpoints := make([]netip.AddrPort, len(node.EndpointsDatabaseField))
 	for idx, ep := range node.EndpointsDatabaseField {