Fix wrong API comment

Summary:
The load method only requires item to be valid, and then fetches it
unconditionally to make sure all required data like tags are present.

Test Plan: Just a change in comments; no testing done

Reviewers: #kde_pim, dvratil

Reviewed By: #kde_pim, dvratil

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D7551