fix(servers): fix plugin segfault when bootscript is null (#2664)

Author: utix

internal/services/instance/servers_data_source.go

@@ -183,7 +183,9 @@ func DataSourceInstanceServersRead(ctx context.Context, d *schema.ResourceData,
 		rawServer["zone"] = string(zone)
 		rawServer["name"] = server.Name
 		rawServer["boot_type"] = server.BootType
-		rawServer["bootscript_id"] = server.Bootscript.ID
+		if server.Bootscript != nil {
+			rawServer["bootscript_id"] = server.Bootscript.ID
+		}
 		rawServer["type"] = server.CommercialType
 		if len(server.Tags) > 0 {
 			rawServer["tags"] = server.Tags