Kai Uwe Broulik authored May 24, 2018 and Eike Hein committed May 24, 2018

Summary:
You cannot compare to `null` but to empty string.
This was done to disable "Pin" when no launcher URL is available but not properly executed in "Start New Instance"

Test Plan:
5.12 branch
* "Launch new instance" is now disabled for e.g. wine notepad where it wouldn't work anyway (second change)
* "Pin" is still properly checked depending on whether the task is pinned or not (first change)

Reviewers: #plasma, hein

Reviewed By: #plasma, hein

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D13069