Broken subscriptions for queries with ASK statement

[GregorioMonari]

Describe the bug
Subscribing to any SEPA engine with a query containing an ASK statment causes unexpected behaviours in the engine

To Reproduce
Steps to reproduce the behaviour:

1. Use any sepa client api, like SEPA-JS
2. Subscribe with this sparql:
   ASK { GRAPH auth:Acl { ?uuid acl:accessTo ?foi; acl:mode acl:Read, acl:Write; acl:agent ?webId } }
3. Perform an update for the previously created subscription

Expected behavior
As a sparql compliant endpoint, the SEPA engine should support the ASK statement for updates, queries and subscriptions.