some simple tasks

[Anton Kreuzkamp]

> Issue: Launchers in Tasks widget disappear after use
> Reference: https://bugs.kde.org/show_bug.cgi?id=278843
> 
> Suggested fixes: either libtaskmanager or the tasks widget are not
> identifying the launcher icon as being available after closing the last
> window. which means something like the icon launcher entry is being lost or
> misidentified. my guess is "misidentified" because they show up on first
> start, but after the app window is shown and then closed, the launcher
> doesn't come back .. until next start.
> 
> Where to start: kde-workspace/libs/taskmanager/
> make sure checkLauncherVisibility in groupmanager.cpp is being called and is
> working properly. easy enough with some kDebug statements and running
> `plasmoidviewer tasks` to test. depending on what that turns up, we can go
> from there.

Fixed this one.