Link and When - Cannot combine object with link

#### Support plan

* *is this issue currently blocking your project?* (yes/no): no
* *is this issue affecting a production system?* (yes/no): no

#### Context

* *node version*: v14.15.5
* *module version*: 17.4.0
* *environment* (e.g. node, browser, native): node
* *used with* (e.g. hapi application, another framework, standalone, ...): standalone
* *any other relevant information*:

#### How can we help?

Hello, thank you for your time. I'm evaluating Joi for replacing AJV, so far so good until I needed to try out one of our recursive schemas. We have modules and templates. Modules has `children` that is a list of resources that can either be a `SubModule` or a `Template`. I was hoping for the following schema to work but I get `Cannot combine object with link` error.

```js
const subModule = Joi.object({
title: Joi.string().required(),
resource: Joi.string().valid("module").required(),
children: Joi.array().items(
Joi.object({
resource: Joi.string().valid("template", "module").required(),
}).when(".resource", {
switch: [
{
is: "module",
then: Joi.link("#subModule"),
},
{
is: "template",
then: template,
},
],
})
),
}).id("subModule");
```

No project files or tests are named. Reproduce the supplied recursive schema in a standalone Node environment using Joi 17.4.0, then inspect how object alternatives, `when`, and `link` are combined. Done means determining whether this schema should be supported and documenting or correcting the resulting behavior with a regression test.

Written by the indexing model from the issue text.