[Debug] Correct output of *::toTestMap(), silence non-error

Summary:
MDB_NOTFOUND is the mdb_cursor_get(.., MDB_NEXT) break condition, not
an actual error.

Correct class name for error output.

Reviewers: Baloo, ngraham

Reviewed By: Baloo, ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D27854