The GraphQL UI cannot be opened if a spring.mvc.servlet.path is configured

The GraphQL UI cannot be opened if a `spring.mvc.servlet.path` is configured like this:

```
spring.mvc.servlet.path=/api
```

Browsing http://localhost:8080/api/graphiql redirects to http://localhost:8080/graphiql?path=/graphql which results in a 404.
Browsing http://localhost:8080/api/graphiql?path=/api/graphql directly works fine.

