Raise a notice for unreachable scope

[Speedy37]

Sometime while writing a query scope, a little mistake is made, a notice about it would be nice

Example:

{
  where: { $instanceOf: "Person" }
  scope: {
     Person: { '.': ['_cats'] },
     Cat: { '.': ['_name'] },
  }
}

Cat can't be a root object, thus the scope defined for Cat is unreachable.