PROV-1025 Don't throw an error if there is no setting for current_location_criteria

Fixes:
```
 Invalid argument supplied for foreach()

providence/app/models/ca_objects.php:1736
providence/app/models/ca_objects.php:1675
providence/app/plugins/relationshipGenerator/relationshipGeneratorPlugin.php:196
providence/app/plugins/relationshipGenerator/relationshipGeneratorPlugin.php:133
providence/app/lib/ca/ApplicationPluginManager.php:70
providence/app/lib/ca/BundlableLabelableBaseModelWithAttributes.php:245
providence/app/lib/ca/BundlableLabelableBaseModelWithAttributes.php:245
providence/tests/plugins/relationshipGenerator/RelationshipGeneratorPluginIntegrationTest.php:280
providence/tests/plugins/relationshipGenerator/RelationshipGeneratorPluginIntegrationTest.php:238
```