NCI-Agency/anet#2954: Fix getRelatedObjectsEngagementAssessments
NCI-Agency/anet#2954: Fix getRelatedObjectsEngagementAssessments

If for a report we had only tasks assessments, it was also
returning a value for attendees assessments. This was not visible
to the user as the returned value was returning empty keys for
entityUuids and therefore was not be used. And therefore we never
noticed this problem before.

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