Bug fix for GlobIterator extending service

Reported by andrer on IRC... If a service extends GlobIterator, there
was a problem where we were checking if (!$instance) which would yield a
catchable fatal error that GlobIterator cannot be casted to a boolean.
To solve this, the comparison operators should be strict so PHP does not
try to convert the type internally. The types checked against are the
expected types if no services have been returned, so the overall
behavior should not be changed by this fix at all.