(PUP-3701) Fix issue with empty exported resources expression

Resources in the catalog were being ignored and only found through the
indirector. This patch fixes that and makes the PuppetDB tests using
this feature pass.
Merge pull request #3344 from senior/ticket/stable/pup-3701-empty-resource-collection-expression

(PUP-3701) Fix issue with empty exported resources expression
Merge branch 'stable'