[taskmanager applet] Fix MPRIS entries in context menu for CanPause==false
Test Plan:
Media player entries Start/Pause show matching state and trigger
expected actions both for VLC & MPRIS-patched Gwenview (CanPause=false).
Reviewers: broulik, hein
Reviewed By: hein
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D11007