Check that IP is set before parsing

Machine is saved to db before it is assigned an ip, so we might have
empty ip fields coming back.

utils.go

@@ -121,6 +121,7 @@ func (h *Headscale) getUsedIPs() ([]netaddr.IP, error) {
 
 	ips := make([]netaddr.IP, len(addresses))
 	for index, addr := range addresses {
+		if addr != "" {
 			ip, err := netaddr.ParseIP(addr)
 			if err != nil {
 				return nil, fmt.Errorf("failed to parse ip from database, %w", err)
@@ -128,6 +129,7 @@ func (h *Headscale) getUsedIPs() ([]netaddr.IP, error) {
 
 			ips[index] = ip
 		}
+	}
 
 	return ips, nil
 }