When adding a yaml-schema that resides in the same workspace as the yaml-files it applies to, it is erroneously validated against itself

Describe the bug

Version 0.17.0.

When you use a YAML-file as a schema in the same workspace as the files you validate reside, the language-server tries to validate the schema against itself. As shown below, globbing does not play into it.

(I have looked at https://github.com/redhat-developer/yaml-language-server/pull/427 which on the surface appeared to be related, but after setting up a test where globbing is not involved, I don't think so.)

Expected Behavior

A YAML schema should not validate against itself, unless specified by the glob pattern.

Current Behavior

A YAML schema validates against itself, even if yaml.schemas association does not specify it.

Steps to Reproduce

1. Create new project in VSCode
2. Add file schema.yaml containing

type: object
properties:
  foo: 
    type: string
    description: A foo property
additionalProperties: false
required: [ 'foo' ]

3. Add file instance.yaml containing

foo: bar

4. Add vscode/settings.json containing

{
    "yaml.schemas": { 
        "http://json-schema.org/draft-07/schema#": ["/schema.yaml"],
        "./schema.yaml": [ "/instance.yaml" ]
    } 
}

Observe:

It is being validated against itself. If you add yet another file instance2.yaml containing

qux: quux

It is, correctly, not being validated against /schema.yaml.

Edit: instance.yaml on the other hand, is, correctly, being validated against `/schema.yaml'

Environment

• Windows
• Mac
• Linux
• other (please specify)

Reproduce the issue with vscode/settings.json, schema.yaml, and instance.yaml using the documented yaml.schemas associations. Start by tracing the language server's schema selection and validation flow for a schema in the same workspace. Done means schema.yaml is not validated against itself unless its association explicitly matches it, while instance.yaml remains validated.