Fixes #16982 - Scope properly when no taxonomies are set

The default scope for hosts and other objects did not restrict
properly by taxonomies. An user without organizations or
locations, could do anything it's permissions allow to.
The list of hosts was unrestricted and showed hosts in
any location or organization.

This is fixed to work so that:

Users without taxonomies, when set to 'any context' cannot see
anything (at all)

Users with taxonomies, when set to 'any context' can see
everything within all of their taxonomies context (including
children taxonomies).

Admins set to 'any context' can see everything - regardless
of whether it has a taxonomy or not.

Users or admins set to some organization/location scope
can only see stuff within scope.