Only add $ref to existing JSON Paths

Consider this output:

{
    "$schema": "http://json-schema.org/draft-07/schema",
    "$id": "http://vanilla-drupal.local/en/jsonapi/block/block/resource/schema.json?XDEBUG_SESSION_START=PHPSTORM",
    "allOf": [
        {
            "type": "object",
            "properties": {
                "attributes": {
                    "$ref": "#/definitions/attributes"
                },
                "relationships": {
                    "$ref": "#/definitions/relationships"
                }
            }
        },
        {
            "$ref": "https://jsonapi.org/schema#/definitions/resource"
        }
    ],
    "properties": {
        "attributes": {
            "$ref": "#/definitions/attributes"
        }
    },
    "definitions": {
        "attributes": {
            "description": "Entity attributes",
            "type": "object",
            "properties": {
                "third_party_settings": {
                    "properties": {
                        "third_party_settings": []
                    }
                },
                "visibility": {
                    "properties": {
                        "visibility": []
                    }
                }
            },
            "additionalProperties": false
        }
    }
}

Notice how /allOf[0]/properties/relationships is pointing to /definitions/relationships. However that path does not exist because this entity type has no relationships.

This won't end up well when de-referencing the schema.