krunner: Prevent regression

Summary:
It was pointed out to me that using NoDisplay=true breaks starting
krunner.

Alternatively D24956 could be landed.

Test Plan: Still works for me, for some reason

Reviewers: Plasma, fvogt

Reviewed By: fvogt

Subscribers: fvogt, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D28853